[readme] Add `propose-update` help output
@@ -185,6 +185,17 @@ Options:
-h, --help Show this message and exit.
```
+```
+$ packit propose-update --help
+Usage: packit propose-update [OPTIONS]
+
+ Release current upstream release into Fedora
+
+Options:
+ --dist-git-branch TEXT Target branch in dist-git to release into.
+ --dist-git-path TEXT Path to dist-git repo to work in.
+ -h, --help Show this message and exit.
+```
## Candidates for early adoption
