In administration documentation about environment variables, point to those for the Go runtime instead of Go compiler (go-gitea#28859)

The previous variables are used by the compiler and aren't too useful
for non-developers. The newly listed variables are more likely to be of
interest.

Apologies for this drive-by PR, I probably missed instructions from the
contributors guide. The patch can be regarded as a simple way to explain
the problem and solution. Feel free to close and possibly create a new
PR that does adhere to the contributors guide.

Author: mjl-

docs/content/administration/environment-variables.en-us.md

@@ -27,14 +27,15 @@ GITEA_CUSTOM=/home/gitea/custom ./gitea web
 
 ## From Go language
 
-As Gitea is written in Go, it uses some Go variables, such as:
+As Gitea is written in Go, it uses some variables that influence the behaviour of Go's runtime, such as:
 
-- `GOOS`
-- `GOARCH`
-- [`GOPATH`](https://golang.org/cmd/go/#hdr-GOPATH_environment_variable)
+- `GOMEMLIMIT`
+- `GOGC`
+- `GOMAXPROCS`
+- `GODEBUG`
 
 For documentation about each of the variables available, refer to the
-[official Go documentation](https://golang.org/cmd/go/#hdr-Environment_variables).
+[official Go documentation on runtime environment variables](https://pkg.go.dev/runtime#hdr-Environment_Variables).
 
 ## Gitea files