Document updating repo:voltha-protos

VERSION
-------
  o Bump version string for the build.
  o https://docs.voltha.org/master/overview/contributing.html?highlight=version#versioning

howto/code/index.rst
howto/code/voltha-protos.rst
----------------------------
  o Begin documenting howto edit volha-protos, commands and dependencies.
  o 'go.mod' urls in the grid are suffixed by a double-underscore to
    notify sphinx/rst document checking that name duplication is OK.

Change-Id: I0abff8c925fa86943c16c9eae8b181b8f0479bd3
diff --git a/VERSION b/VERSION
index 8d81fbf..ae93586 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.12.6-dev3
+2.12.7