Add SSH troubleshooting section to DevContainers article

Author: skrysm

content/articles/containers/devcontainers.md

@@ -112,3 +112,31 @@ RUN apk add --no-cache git-lfs
 
 EXPOSE 1313
 ```
+
+## SSH Troubleshooting
+
+Normally, VSCode *automatically* forwards the host's ssh-agent into the DevContainer. Here's how this normally works and that can give you a hint at where the problem is.
+
+To see, if ssh works inside the devcontainer (i.e. the ssh-agent from the host is correctly routed to the container), execute:
+
+```sh
+$ ssh-add -l
+4096 SHA256:WJ2WxTG1F4bHWq29eN+lvc/5VYLhjAZp5b5555PkGis Primary SSH Key (RSA)
+```
+
+If this gives you an error, check `$SSH_AUTH_SOCK`:
+
+```sh
+$ echo $SSH_AUTH_SOCK
+/tmp/vscode-ssh-auth-2d206968-2061-406b-8a9f-a4a2249dc649.sock
+```
+
+If this variable is empty, search the contents of the container log (F1 > Dev Containers: Show Container Log) for "SSH_AUTH_SOCK":
+
+```
+[16730 ms] Start: Launching Dev Containers helper.
+[16730 ms] ssh-agent: SSH_AUTH_SOCK not set on local host.
+[16732 ms] ssh-agent: SSH_AUTH_SOCK in container (/tmp/vscode-ssh-auth-2d206968-2061-406b-8a9f-a4a5349dc649.sock) forwarded to local host (\\.\pipe\openssh-ssh-agent).
+```
+
+If this doesn't work and you are on Windows, it *may* help to manually set the `SSH_AUTH_SOCK` environment variable to `\\.\pipe\openssh-ssh-agent` ([source](https://github.com/microsoft/vscode-remote-release/issues/11043#issuecomment-3005677524)).