Update Dockerfile

#3

Author: cicirello

Dockerfile

@@ -1,6 +1,13 @@
+# If all you need is Python 3, use:
 FROM cicirello/pyaction-lite:3
+
+# If you need Python 3 and the GitHub CLI, then use:
 # FROM cicirello/pyaction:4
+
+# If Python 3 + git is sufficient, then use:
 # FROM cicirello/pyaction:3
+
+# To pull from the GitHub Container Registry instead, use one of these:
 # FROM ghcr.io/cicirello/pyaction-lite:3
 # FROM ghcr.io/cicirello/pyaction:4
 # FROM ghcr.io/cicirello/pyaction:3