feat(cdr): Docs for remote postgresql C4D (#818)

Author: Emyrk

setup/docker.md

@@ -91,6 +91,45 @@ For example:
 docker run --rm -it -p 7080:7080 -v /var/run/docker.sock:/var/run/docker.sock -v ~/.coder:/var/run/coder -e DEVURL_HOST="*.mycompany.com" codercom/coder:1.27.0
 ```
 
+## Use an external PostgreSQL database
+
+If you'd like to use an external database, you must:
+
+1. Disable the embedded database by setting the `DB_EMBEDDED` environment
+   variable (see the next code snippet for an example)
+1. Provide the connection information to the external PostgreSQL database:
+
+   ```console
+   docker run --rm -it -p 7080:7080 \
+      -v /var/run/docker.sock:/var/run/docker.sock \
+      -v ~/.coder:/var/run/coder \
+      # Disable using the embedded DB
+      -e DB_EMBEDDED="" \
+      # Change these values to match those for your database
+      -e DB_HOST=127.0.0.1 \
+      -e DB_PORT=5432 \
+      -e DB_USER=postgres \
+      -e DB_PASSWORD="" \
+      -e DB_NAME=postgres \
+      -e DB_SSL_MODE=disable \
+      codercom/coder:1.27.0
+   ```
+
+Coder supports client TLS certificates using `DB_SSL_MODE=verify-full`. Ensure
+that you mount the certs into the container (and add the flag
+`-v <local_certs>:/certs`). Then, specify the certificate path using environment
+variables:
+
+<!-- markdownlint-disable -->
+
+| **Flag/environment variable**     | **Description**                              |
+| --------------------------------- | -------------------------------------------- |
+| `-e DB_CERT=/certs/client.crt`    | The path to the client cert signed by the CA |
+| `-e DB_KEY=/certs/client.key`     | The path to the client secret                |
+| `-e DB_ROOT_CERT=/certs/myCA.crt` | The path to the trusted CA cert              |
+
+<!-- markdownlint-enable -->
+
 ## Admin password
 
 If you want to set (or reset) your admin password, use the
@@ -108,7 +147,6 @@ For organizations, we recommend one Docker host per team of 5-10 developers.
 
 Currently, Coder for Docker does not support:
 
-- External PostgreSQL databases
 - The use of your own TLS certificates. If you'd like to use TLS with Coder for
   Docker, you'll need to run Coder behind a reverse proxy (e.g., Caddy or NGINX)
   and terminate TLS at that point. See