Added a HOWTO page release based source edits.

conf.py
-------
   * Exclude all variants of python virtual env from traversal.
   * Exclude __pycache__ from document traversal.

index.rst
---------
   * Create a top level index link/page for release howto(s).

overview/contributing.rst
-------------------------
   * Document version based script edits required at time of release.
   * This URL will be used by repo:ci-management/vars/installVoltctl
     to display self-documenting help.

*/urls
------
   * Added placeholders and resources for documenting future topics.

Chaser edits:
-------------
   o Bump VERSION string.
   o 'stern' URL in unrelated troublteshooting.rst doc failed link check:
      + github repo no longer exists.
      + add replacement github/stern/stern

Change-Id: I2f0f15eb5ba7bd6817806296928964df5259b21a
diff --git a/conf.py b/conf.py
index 8cb9c93..a0a0a96 100644
--- a/conf.py
+++ b/conf.py
@@ -114,8 +114,6 @@
         '.DS_Store',
         'Thumbs.db',
         '_build',
-        'venv_docs',
-        'voltha-system-tests/vst_venv',
         'voltha-go/BUILD.md',
         'cord-tester/venv_cord',
         'cord-tester/docs',
@@ -128,7 +126,13 @@
         'bbsim/README.md',
         'CODE_OF_CONDUCT.md',
         '*/CODE_OF_CONDUCT.md',
-        'doc_venv/*'
+# Ignore all:
+        '**/__pycache__', # generated - faster traversal
+# Revisit: one directory pattern is sufficient.
+        '**/doc_venv',
+        '**/venv_docs',
+        '**/virtualenv',
+        '**/vst_venv',
 ]
 
 # The name of the Pygments (syntax highlighting) style to use.