Add Prerequisites (#5734)

Add set system user guide.
Add absolute path for sqlite3 guide.

docs/content/doc/installation/windows-service.en-us.md

@@ -13,6 +13,27 @@ menu:
     identifier: "windows-service"
 ---
 
+# Prerequisites
+
+The following changes are made in C:\gitea\custom\conf\app.ini:
+
+```
+RUN_USER = COMPUTERNAME$
+```
+
+Sets Gitea to run as the local system user.
+
+COMPUTERNAME is whatever the response is from `echo %COMPUTERNAME%` on the command line. If the response is `USER-PC` then `RUN_USER = USER-PC$`
+
+## Use absolute paths
+
+If you use sqlite3, change the `PATH` to include the full path:
+
+```
+[database]
+PATH     = c:/gitea/data/gitea.db
+```
+
 # Register as a Windows Service
 
 To register Gitea as a Windows service, open a command prompt (cmd) as an Administrator,