MFC: tweak the langauge

Don't say there are two options and then give only one. Update that
sentence to reflect where the project seems to have landed in terms of
how to do MFCs.  The original was written prior to the transtion and the
existing practice has shifted to cherry-pick -x almost exclusively.

documentation/content/en/articles/committers-guide/_index.adoc

@@ -861,8 +861,7 @@ There are a few options for resolving this:
 ==== Commit message standards
 ===== Marking MFCs
 
-There are two main options for marking MFCs as distinct from direct
-commits:
+The project has adopted the following practice for marking MFCs:
 
 * Use the `-x` flag with `git cherry-pick`.  This adds a line to the
   commit message that includes the hash of the original commit when