Refine wording in SourceLevelDebugPkg/Readme.txt.

Signed-off-by: niruiyu
Reviewed-by: vanjeff

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12857 6f19259b-4bc3-4df7-8a09-765794883524
1 file changed