[Flang] Add GettingInvolved documentation page and sidebar.

Adds a new GettingInvolved page to documentation which provides details about
mailing list, chats and calls.

Adds a sidebar page which provides common links on
all documentation pages.
The links include:
-  Getting Started
-  Getting Involved
-  Github Repository
-  Bug Reports
-  Code Review

Depends on https://reviews.llvm.org/D87242

Reviewed By: richard.barton.arm

Differential Revision: https://reviews.llvm.org/D87270

flang/docs/GettingInvolved.md

@@ -0,0 +1,72 @@
+<!--===- docs/GettingInvolved.md
+
+   Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+   See https://llvm.org/LICENSE.txt for license information.
+   SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+-->
+# Getting Involved
+
+```eval_rst
+.. contents::
+   :local:
+```
+
+The Flang Project welcomes contributions of all kinds.
+Please feel free to join the mailing list or the slack channel for discussions related to development of Flang.
+To understand the status of various developments in Flang please join the respective call.
+
+## Mailing Lists
+
+[Developer's List (flang-dev)](http://lists.llvm.org/mailman/listinfo/flang-dev)
+
+  This list is for people who want to be included in technical discussions related to Flang. People post to this list when they have questions about writing code
+  for or using the Flang tools. It is relatively low volume.
+
+
+[Commits Archive (flang-commits)](http://lists.llvm.org/pipermail/flang-commits)
+
+  This list contains all commit messages that are made when Flang developers
+  commit code changes to the repository. It also serves as a forum for
+  patch review (i.e. send patches here). It is useful for those who want to
+  stay on the bleeding edge of Flang development. This list is high
+  volume.
+
+## Chat
+
+### Flang Slack Workspace
+
+-   There is a Slack workspace dedicated to Flang.
+-   There are a number of topic-oriented channels available (e.g., #driver, #f18-semantics, #fir).
+-   Add yourself via the *[invitation link](https://join.slack.com/t/flang-compiler/shared_invite/zt-2pcn51lh-VrRQL_YUOkxA_1CEfMGQhw "title")*
+
+## Calls
+
+### Flang Community Biweekly Call
+
+-   General updates on the Flang Project, both LLVM Flang and current Flang.
+-   Join [Flang Community Biweekly Call](https://nvmeet.webex.com/nvmeet/j.php?MTID=mb4edb8c799f69ec2dc0554acc969a162)
+-   Time: On Wednesdays 8:30 Pacific Time, on the weeks alternating with regular Flang Community Technical Biweekly Call.
+-   Minutes: They are sent to [flang-dev](http://lists.llvm.org/mailman/listinfo/flang-dev). Search for `Flang Biweekly Sync - Notes`.
+
+### Flang Community Technical Biweekly Call
+
+-   Technical topics call.
+-   Join [Flang Community Technical Biweekly Call](https://bluejeans.com/625064848?src=join_info)
+-   Time: On Mondays 8:30 Pacific Time, on the weeks alternating with regular Flang Community Biweekly Call.
+-   The agenda is in this [Google Doc](https://docs.google.com/document/d/1Z2U5UAtJ-Dag5wlMaLaW1KRmNgENNAYynJqLW2j2AZQ/).
+
+### LLVM Alias Analysis Technical Call
+
+-   For people working on improvements to LLVM alias analysis.
+-   Join [LLVM Alias Analysis Technical Call](https://bluejeans.com/101176001?src=join_info)
+-   Time: Tuesdays 10:00 AM Pacific Time, every 4 weeks.
+-   The agenda is in this [Google Doc](https://docs.google.com/document/d/1ybwEKDVtIbhIhK50qYtwKsL50K-NvB6LfuBsfepBZ9Y/).
+
+### OpenMP Technical Call
+
+-   Development updates on OpenMP and OpenACC in the Flang Project.
+-   Join [OpenMP Technical Call](https://bit.ly/39eQW3o)
+-   Time: Weekly call on every Thursdays 8:00 AM Pacific time.
+-   Meeting minutes are [here](https://docs.google.com/document/d/1yA-MeJf6RYY-ZXpdol0t7YoDoqtwAyBhFLr5thu5pFI).
+-   Status tracking [page](https://docs.google.com/spreadsheets/d/1FvHPuSkGbl4mQZRAwCIndvQx9dQboffiD-xD0oqxgU0/edit#gid=0).

flang/docs/_templates/indexsidebar.html

@@ -0,0 +1,26 @@
+{# This template defines sidebar which can be used to provide common links on
+   all documentation pages. #}
+
+<h3>Documentation</h3>
+
+<ul class="want-points">
+    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/README.md#getting-started">Getting Started</a></li>
+</ul>
+
+<h3>Getting Involved</h3>
+<! TODO: Point links to website(flang.llvm.org) and not github once webpage comes up.>
+<ul class="want-points">
+    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/docs/GettingInvolved.md#mailing-lists">Mailing Lists</a></li>
+    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/docs/GettingInvolved.md#chat">Slack</a></li>
+    <li><a href="https://github.com/llvm/llvm-project/blob/master/flang/docs/GettingInvolved.md#calls">Calls</a></li>
+</ul>
+
+<h3>Additional Links</h3>
+
+<ul class="want-points">
+    <li><a href="https://github.com/llvm/llvm-project/tree/master/flang/">Github Repository</a></li>
+    <li><a href="https://bugs.llvm.org/">Bug Reports</a></li>
+    <li><a href="https://reviews.llvm.org/">Code Review</a></li>
+<! TODO: Have the bots setup first>
+    <li><a href="#">Doxygen API</a></li>
+</ul>

flang/docs/_templates/layout.html

@@ -0,0 +1,14 @@
+{% extends "!layout.html" %}
+
+{% block extrahead %}
+<style type="text/css">
+  table.right { float: right; margin-left: 20px; }
+  table.right td { border: 1px solid #ccc; }
+</style>
+{% endblock %}
+
+{% block rootrellink %}
+<! TODO: Change the webpage  >
+  <li><a href="https://flang.llvm.org">Flang Home</a>&nbsp;|&nbsp;</li>
+  <li><a href="{{ pathto('index') }}">Documentation</a>&raquo;</li>
+{% endblock %}

flang/docs/conf.py

@@ -167,7 +167,13 @@ html_last_updated_fmt = '%b %d, %Y'
 #html_use_smartypants = True
 
 # Custom sidebar templates, maps document names to template names.
-#html_sidebars = {}
+html_sidebars = {
+    '**': [
+        'indexsidebar.html',
+        'searchbox.html',
+    ]
+}
+
 
 # Additional templates that should be rendered to pages, maps page names to
 # template names.

flang/docs/index.md

@@ -15,6 +15,7 @@ Flang is LLVM's Fortran frontend
 .. toctree::
    :titlesonly:
 
+   GettingInvolved
    FortranForCProgrammers
    C++style
    C++17