gnucash unstable: Clarify cmake build directory location and source path.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/07ba7a3a (commit)
	from  https://github.com/Gnucash/gnucash/commit/6c619400 (commit)



commit 07ba7a3a9893e3bc9a9568b5b22c277149a9ee35
Author: John Ralls <jralls at ceridwen.us>
Date:   Thu Apr 5 16:50:32 2018 -0700

    Clarify cmake build directory location and source path.



Summary of changes:
 cmake/README_CMAKE.txt | 40 +++++++++++++++++++++++++++++-----------
 1 file changed, 29 insertions(+), 11 deletions(-)