Fixed several sphinx WARNINGS, added more release text

Change-Id: Ia167a9d46ee48fbf27c6cd09d78fcf31f3d4aedf
diff --git a/howto/release/index.rst b/howto/release/index.rst
index ce276ee..e1d998c 100644
--- a/howto/release/index.rst
+++ b/howto/release/index.rst
@@ -20,3 +20,7 @@
    voltctl/install
    voltctl/release
    voltctl/see_also
+
+   checklist
+   scripts/preparation
+   scripts/repository-voltha-release