devcontainer.json: symlink workspace to /simbricks

This results in the same environment as with the provided dockerfiles.
Then we can use that as the default setting for the instantiation
environment.

.devcontainer.json

@@ -17,5 +17,6 @@
 	"remoteEnv": {
 		"PATH": "/home/simbricks/.local/bin:${containerEnv:PATH}"
 	},
+	"postCreateCommand": "sudo ln -s `pwd` /simbricks",
 	"postStartCommand": "sudo chmod o+rw /dev/kvm"
 }