add documentation for all used configuration variables
Some configuration options are only available through setting environment variables.
| **Option** | **Type** | **Description** |
-| -------------------- | ---------| --------------- |
+|-------------------------|----------|--------------------------------------------------------------------------------------------------------------|
| `CHECKPOINT_DISABLE` | `bool` | Set to any non-empty value to disable calling the GitHub API when running `gopass version`. |
| `GOPASS_DEBUG` | `bool` | Set to any non-empty value to enable verbose debug output |
| `GOPASS_UMASK` | `octal` | Set to any valid umask to mask bits of files created by gopass |
| `GOPASS_GPG_OPTS` | `string` | Add any extra arguments, e.g. `--armor` you want to pass to GPG on every invocation |
+| `GOPASS_EXTERNAL_PWGEN` | `string` | Use an external password generator. See [Features](features.md#using-custom-password-generators) for details |
+| `GOPASS_NOCOLOR` | `bool` | Set to true to disable colored output |
+| `GOPASS_CHARACTER_SET` | `bool` | Set to any non-empty value to restrict the characters used in generated passwords |
+| `GOPASS_CONFIG` | `string` | Set this to the absolute path to the configuration file |
+| `GOPASS_HOMEDIR` | `string` | Set this to the absolute path of the directory containing the `.config/` tree |
+| `GOPASS_FORCE_UPDATE` | `bool` | Set to any non-empty value to force an update (if available) |
+| `GOPASS_NO_NOTIFY` | `bool` | Set to any non-empty value to prevent notifications |
+
+Variables not exclusively used by gopass
+
+| **Option** | **Type** | **Description** |
+|------------------------|----------|--------------------------------------------------------------------------------------------------------|
+| `PASSWORD_STORE` | `string` | absolute path containing the password store (a directory) |
+| `PASSWORD_STORE_UMASK` | `string` | Set to any valid umask to mask bits of files created by gopass (GOPASS_UMASK has precedence over this) |
+| `EDITOR` | `string` | command name to execute for editing password entries |
+| `PAGER` | `string` | the pager program used for `gopass list`. See [Features](features.md#auto-pager) for details |
+| `GIT_AUTHOR_NAME` | `string` | name of the author, used by the rcs backend to create a commit |
+| `GIT_AUTHOR_EMAIL` | `string` | email of the author, used by the rcs backend to create a commit |
## Configuration Options
