docs: add documentation about the offline docs (coder#8603)

Author: BrunoQuaresma

docs/install/offline.md

@@ -185,3 +185,15 @@ coder:
       value: ""
 # ...
 ```
+
+## Offline docs
+
+Coder also provides offline documentation in case you want to host it on your own server. The docs are exported as static files that you can host on any web server, as demonstrated in the example below:
+
+1. Go to the release page. In this case, we want to use the [latest version](https://github.com/coder/coder/releases/latest).
+2. Download the documentation files from the "Assets" section. It is named as `coder_docs_<version>.tgz`.
+3. Extract the file and move its contents to your server folder.
+4. If you are using NodeJS, you can execute the following command: `cd docs && npx http-server .`
+5. Set the `CODER_DOCS_URL` environment variable to use the URL of your hosted docs. This way, the Coder UI will reference the documentation from your specified URL.
+
+With these steps, you'll have the Coder documentation hosted on your server and accessible for your team to use.