docs: Explicit restrictions of atlantis user apply to the --data-dir …

…flag (#2915)

* Change the directory mentioned in the `--data-dir` flag description

* Be more explicit on how restrictions of the atlantis user may apply to the `--data-dir` flag

* wrap flag in quotes

* `Please note` -> `Note`

* revert back to `~/atlantis`

* Update server-configuration.md

runatlantis.io/docs/server-configuration.md

@@ -321,6 +321,9 @@ and set `--autoplan-modules` to `false`.
   Terraform binaries here. If Atlantis loses this directory, [locks](locking.html)
   will be lost and unapplied plans will be lost.
 
+  Note that the atlantis user is restricted to `~/.atlantis`. 
+  If you set the `--data-dir` flag to a path outside of Atlantis its home directory, ensure that you grant the atlantis user the correct permissions.
+
 ### `--default-tf-version`
   ```bash
   atlantis server --default-tf-version="v0.12.31"