docs(README): Move Environment variables above build args

Signed-off-by: Sebastian Hasler <sebastian.hasler@stuvus.uni-stuttgart.de>

README.md

@@ -13,6 +13,13 @@ as follows.
 docker build --build-arg BASE=docker.io/sharelatex/sharelatex:2.6.1 -t docker-overleaf-ldap .
 ```
 
+## Environment variables
+
+Two environment variables are used at runtime to configure the bind user:
+
+- `LDAP_BIND_USER`: Bind-DN, i.e., DN of the bind user.
+- `LDAP_BIND_PW`: Password of the bind user.
+
 ## Build arguments
 
 The following arguments can be passed via `--build-args`.
@@ -22,12 +29,6 @@ The following arguments can be passed via `--build-args`.
 | `BASE`            | `docker.io/sharelatex/sharelatex`                                     | Can be set to any Overleaf image tag. See [here](https://hub.docker.com/r/sharelatex/sharelatex/tags?page=1&ordering=last_updated) for a list of tags. |
 | `LDAP_PLUGIN_URL` | `https://codeload.github.com/smhaller/ldap-overleaf-sl/tar.gz/master` | URL to download ldap-overleaf-sl from.                                                                                                                 |
 
-## Environment variables
-
-Two environment variables are used to configure the bind user:
-
-- `LDAP_BIND_USER`: Bind-DN, i.e., DN of the bind user.
-- `LDAP_BIND_PW`: Password of the bind user.
 ## GitLab CI
 
 The `environment` file is used to specify some environment variables for the GitLab CI: