[NFC][docs] Fix link.

The rendered html was (no hyperlink was generated):

(see Getting Started <GettingStarted.html#git-pre-push-hook>)

Now, it is (with proper hyperlink):

(see Git pre-push hook)

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D88116

llvm/docs/GettingStarted.rst

@@ -528,6 +528,9 @@ that include merges, so the `git rebase` step above is required.
 
 Please ask for help if you're having trouble with your particular git workflow.
 
+
+.. _git_pre_push_hook:
+
 Git pre-push hook
 ^^^^^^^^^^^^^^^^^
 

llvm/docs/Phabricator.rst

@@ -187,7 +187,7 @@ this reason avoid using `arc land` and push commits to master directly with git
 after removing tags other than "Reviewed by" and "Differential Revision".
 You can run `llvm/utils/git/arcfilter.sh` to clean the commit message of the
 current "HEAD" commit automatically. You can also setup a git hook to catch this
-for you (see `Getting Started <GettingStarted.html#git-pre-push-hook>`).
+for you (see :ref:`git_pre_push_hook`).
 
 
 Committing someone's change from Phabricator