misc: Add KCONFIG.md file which talks about Kconfig files.

There are some minor aspects about how Kconfig files are used in gem5
which are a little different from how they are documented online or are
used in other projects. Document that in this file.

Change-Id: Ib981d1e265cf466d453071b33820d6baa24e17d4
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58634
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed