crane/gcrane: add pages (#13853)

pages/common/gcrane-gc.md

@@ -0,0 +1,18 @@
+# gcrane gc
+
+> List images that are not tagged.
+> Will calculate images that can be garbage-collected.
+> This can be composed with `gcrane delete` to actually garbage collect them.
+> More information: <https://github.com/google/go-containerregistry/blob/main/cmd/gcrane/README.md>.
+
+- List untagged images:
+
+`gcrane gc {{repository}}`
+
+- Whether to recurse through repositories:
+
+`gcrane gc {{repository}} {{-r|--recursive}}`
+
+- Display help:
+
+`gcrane gc {{-h|--help}}`