docs: update docs for new gpg forwarding feature

Signed-off-by: Luca Di Maio <luca.dimaio1@gmail.com>

docs/pages/developing-in-workspaces/credentials.mdx

@@ -23,4 +23,20 @@ DevPod will make docker registry credentials available inside the dev container
 If you don't want DevPod to inject the credentials, you can disable that via the following command for all workspaces:
 ```
 devpod context set-options default -o INJECT_DOCKER_CREDENTIALS=false
-```
+```
+
+## GPG credentials
+
+DevPod will gpg keys available inside the dev container through an ssh tunnel. This allows you to sign commits from inside the workspace.
+
+If you want DevPod to inject the gpg keys, you must that via the following command for all workspaces:
+```
+devpod context set-options default -o GPG_AGENT_FORWARDING=true
+```
+
+Or when creating a workspace using:
+
+```
+devpod up --gpg-agent-forwarding my-workspace
+```
+