relnotes: add entry for `hg diff --merge -c`
Differential Revision: https://phab.mercurial-scm.org/D9944
Welcome to Mercurial for Windows!
---------------------------------
For configuration and usage directions, please read the ReadMe.html
file that comes with this package.
Also check the release notes at:
https://mercurial-scm.org/wiki/WhatsNew