update readme
Add ChangeLog creation to create-release-tag.sh

- Add automatic creation and commiting of ChangeLog
Rename create-release-tag.sh to create-release.sh #111
Fix bugs in create-release.sh #111
Create Release: rel2013_08_06.15.01.46
Remove old train/stage tag create scripts #111
Improve documentation on new release process, #111
Merge pull request #112 from mozilla/111-improve-release-process

Add create-release.sh and improve docs