Add GITEA_CUSTOM configuration in customization section (#111)

* Add GITEA_CUSTOM configuration in customization section

* Add new section about Gitea specific environment variables

* Revert "Add GITEA_CUSTOM configuration in customization section"

This reverts commit b077702.

content/doc/advanced/specific-variables.en-us.md

@@ -0,0 +1,67 @@
+---
+date: "2017-04-08T11:34:00+02:00"
+title: "Specific variables"
+slug: "specific-variables"
+weight: 20
+toc: false
+draft: false
+menu:
+  sidebar:
+    parent: "advanced"
+    name: "Specific variables"
+    weight: 20
+    identifier: "specific-variables"
+---
+
+# Specific variables
+
+This is an inventory of Gitea environment variables. They change Gitea behaviour.
+
+Initialize them before Gitea command to be effective, for example:
+
+```
+GITEA_CUSTOM=/home/gitea/custom ./gitea web
+```
+
+## From Go language
+
+As Gitea is written in Go, it uses some Go variables as:
+
+  * `GOOS`
+  * `GOARCH`
+  * `GOPATH`
+
+For `GOPATH`, check [official documentation about GOPATH environment variable](https://golang.org/cmd/go/#hdr-GOPATH_environment_variable).
+
+For others, check [official documentation about variables used when it runs the generator](https://golang.org/cmd/go/#hdr-Generate_Go_files_by_processing_source).
+
+## Gitea files
+
+  * `GITEA_WORK_DIR`: Gitea absolute path of work directory.
+  * `GITEA_CUSTOM`: Gitea uses `GITEA_WORK_DIR`/custom folder by default. Use this variable to change *custom* directory.
+  * `GOGS_WORK_DIR`: Deprecated, use `GITEA_WORK_DIR`
+  * `GOGS_CUSTOM`: Deprecated, use `GITEA_CUSTOM`
+
+## Operating system specifics
+
+  * `USER`: system user that launch Gitea. Useful for repository URL address on Gitea interface
+  * `USERNAME`: if no USER found, Gitea will try `USERNAME`
+  * `HOME`: User home directory path (**except if** you're running on Windows, check  the following `USERPROFILE` variable)
+
+### Only on Windows
+
+  * `USERPROFILE`: User home directory path. If empty, uses `HOMEDRIVE` + `HOMEPATH`
+  * `HOMEDRIVE`: Main drive path you will use to get home directory
+  * `HOMEPATH`: Home relative path in the given home drive path
+
+## Macaron (framework used by Gitea)
+
+  * `HOST`: Host Macaron will listen on
+  * `PORT`: Port Macaron will listen on
+  * `MACARON_ENV`: global variable to provide special functionality for development environments vs production environments. If MACARON_ENV is set to "" or "development" then templates will be recompiled on every request. For more performance, set the MACARON_ENV environment variable to "production".
+
+## Miscellaneous
+
+  * `SKIP_MINWINSVC`: Do not run as a service on Windows if set to 1
+  * `ZOOKEEPER_PATH`: [Zookeeper](http://zookeeper.apache.org/) jar file path
+