Added a warning

Embedding.md

@@ -1,3 +1,5 @@
+# WARNING: Until issue #173 goes through, the [core][1] repository will not be up-to-date with the latest changes and fixes, but can still be used.
+
 If you want to use TMK for your own keyboard project, you've got three options for embedding the [core][1].  
 The recommended option is [subtrees](#1-git-subtree).