change PIDFile default from /var/run/gitea.pid to /run/gitea.pid (#12500)

* docs: update heading

This section covers more paths than the 3 listed in the heading.

* setting: change PIDFile default from /var/run/gitea.pid to /run/gitea.pid

On most modern distributions, /var/run is deprecated and only kept for
backwards compat according to
https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch05s13.html, and is a
symlink to `/run/` on modern distributions.

Old Distros that still don't have `/run` can update the gitea default as
described in from-source.en-us.md to point to the old location.

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

docs/content/doc/installation/from-source.en-us.md

@@ -137,7 +137,7 @@ launched manually from command line, it can be killed by pressing `Ctrl + C`.
 ./gitea web
 ```
 
-## Changing the default CustomPath, CustomConf and AppWorkPath
+## Changing default paths
 
 Gitea will search for a number of things from the `CustomPath`. By default this is
 the `custom/` directory in the current working directory when running Gitea. It will also

modules/setting/setting.go

@@ -375,7 +375,7 @@ var (
 	Cfg           *ini.File
 	CustomPath    string // Custom directory path
 	CustomConf    string
-	PIDFile       = "/var/run/gitea.pid"
+	PIDFile       = "/run/gitea.pid"
 	WritePIDFile  bool
 	ProdMode      bool
 	RunUser       string