makefile: fix lib/transform docs not getting updated

As of
https://github.com/rclone/rclone/commit/4280ec75ccfd27fbc4f646d5323b8ed060062be5
the lib/transform docs are generated with //go:generate and embedded with
//go:embed.

Before this change, however, they were not getting automatically updated with
subsequent changes (like
https://github.com/rclone/rclone/commit/fe62a2bb4ea8f62a1567c7883c0bba81827656eb)
because `go generate ./lib/transform` was not being run as part of the release
making process.

This change fixes that by running it in `make commanddocs`.

Makefile

@@ -145,6 +145,7 @@ MANUAL.txt:	MANUAL.md
 	pandoc -s --from markdown-smart --to plain MANUAL.md -o MANUAL.txt
 
 commanddocs: rclone
+	go generate ./lib/transform
 	-@rmdir -p '$$HOME/.config/rclone'
 	XDG_CACHE_HOME="" XDG_CONFIG_HOME="" HOME="\$$HOME" USER="\$$USER" rclone gendocs --config=/notfound docs/content/
 	@[ ! -e '$$HOME' ] || (echo 'Error: created unwanted directory named $$HOME' && exit 1)