Tell people about update bug in README/issue template.

.github/ISSUE_TEMPLATE.md

+If Homebrew was updated on Aug 10-11th 2016 and `brew update` always says `Already up-to-date.` you need to run: `cd $(brew --repo); git fetch; git reset --hard origin/master; brew update`.
+
 # Please follow the general troubleshooting steps first:
 
 - [ ] Ran `brew update` and retried your prior step?

README.md

 # Homebrew
 Features, usage and installation instructions are [summarised on the homepage](http://brew.sh).
 
+## Update Bug
+If Homebrew was updated on Aug 10-11th 2016 and `brew update` always says `Already up-to-date.` you need to run:
+```bash
+cd $(brew --repo); git fetch; git reset --hard origin/master; brew update
+```
+
 ## What Packages Are Available?
 1. Type `brew search` for a list.
 2. Or visit [braumeister.org](http://braumeister.org) to browse packages online.