mk/developer.mk: reorganize documentation for 'make cce'

In most cases, the command 'make cce' is all that is needed to add a
changes entry, so put it at the top of the documentation.  The smaller
steps are useful when updating multiple packages at once, which is less
often the case.

Make the possible values for CTYPE stand out, instead of hiding them in
the body text.

(rillig)