Add version v28 (#564)

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Reviewed-on: https://gitea.com/gitea/docs/pulls/564
Reviewed-by: bircni <[email protected]>
Co-authored-by: Lunny Xiao <[email protected]>

versioned_docs/version-28/administration/environment-variables.md

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+---
+date: "2017-04-08T11:34:00+02:00"
+slug: "environment-variables"
+sidebar_position: 10
+aliases:
+  - /en-us/environment-variables
+---
+
+# Environment variables
+
+This is an inventory of Gitea environment variables. They change Gitea behaviour.
+
+Initialize them before Gitea command to be effective, for example:
+
+```sh
+GITEA_CUSTOM=/home/gitea/custom ./gitea web
+```
+
+## From Go language
+
+As Gitea is written in Go, it uses some variables that influence the behaviour of Go's runtime, such as:
+
+- `GOMEMLIMIT`
+- `GOGC`
+- `GOMAXPROCS`
+- `GODEBUG`
+
+For documentation about each of the variables available, refer to the
+[official Go documentation on runtime environment variables](https://pkg.go.dev/runtime#hdr-Environment_Variables).
+
+## Gitea files
+
+- `GITEA_WORK_DIR`: Absolute path of working directory.
+- `GITEA_CUSTOM`: Gitea uses `WorkPath`/custom folder by default. Use this variable to change _custom_ directory.
+
+## Operating system specifics
+
+- `USER`: System user that Gitea will run as. Used for some repository access strings.
+- `USERNAME`: if no `USER` found, Gitea will use `USERNAME`
+- `HOME`: User home directory path. The `USERPROFILE` environment variable is used in Windows.
+
+### Only on Windows
+
+- `USERPROFILE`: User home directory path. If empty, uses `HOMEDRIVE` + `HOMEPATH`
+- `HOMEDRIVE`: Main drive path used to access the home directory (C:)
+- `HOMEPATH`: Home relative path in the given home drive path
+
+## Miscellaneous
+
+- `SKIP_MINWINSVC`: If set to 1, do not run as a service on Windows.