stable: initial stable-branching documentation

It is expected that this document will change over time. This
represents an initial starting point as we create and release
our stable branches.

Fixes: kata-containers#237

Signed-off-by: Eric Ernst <eric.ernst@intel.com>

Stable-Branch-Strategy.md

@@ -8,6 +8,11 @@ the project, we will introduce many new features which will require a minor vers
 as well as bug fixes.  To facilitate a stable user environment, Kata will begin to provide
 stable branch based releases as well as a master branch release.
 
+## Stable branch patch criteria
+
+No new features should be introduced to stable branches.  The intention is to limit risk to users,
+providing only bug and security fixes.
+
 ## Branch Management
 Kata Containers will maintain two stable release branches in addition to the master branch.
 Once a new MAJOR or MINOR release is created off of master, a new stable branch will be created for