meta-beagle: Add SECURITY file

Add missing SECURITY file required by yocto-check-layer.

Signed-off-by: Ryan Eatmon <reatmon@ti.com>

meta-beagle/SECURITY

@@ -0,0 +1,20 @@
+How to Report a Potential Vulnerability?
+========================================
+
+If you would like to report a public issue (for example, one with a released
+CVE number), please report it to the mailing list:
+
+  https://lists.yoctoproject.org/g/meta-ti
+
+If you are dealing with a not-yet released or urgent issue, please send a
+message to one of the maintainers listed in the README.  Include as many
+details as possible:
+  - the layer or software module affected
+  - the recipe and its version
+  - any example code, if available
+
+Branches maintained with security fixes
+---------------------------------------
+
+See https://wiki.yoctoproject.org/wiki/Releases for the list of current
+releases.  We only accept patches for the LTS releases and the master branch.