Add cheat for documented but not visible negative and merged filters.

README.md

@@ -23,6 +23,8 @@ A collection of cool hidden and not so hidden features of Git and GitHub. This c
   - [Cross-Link Issues](#cross-link-issues)
   - [Locking Conversations](#locking-conversations)
   - [CI Status on Pull Requests](#ci-status-on-pull-requests)
+  - [Negative filters in Issues](#negative-filters-in-issues)
+  - [Merged pull requests filter](#merged-pull-requests-filter)
   - [Syntax Highlighting in Markdown Files](#syntax-highlighting-in-markdown-files)
   - [Emojis](#emojis)
   - [Images/GIFs](#imagesgifs)
@@ -284,6 +286,33 @@ If set up correctly, every time you receive a Pull Request, [Travis CI](https://
 
 [*Read more about the commit status API.*](https://github.com/blog/1227-commit-status-api)
 
+### Negative filters in Issues
+
+Both issues and pull requests allow filtering in the user interface.
+
+For the Rails repo: https://github.com/rails/rails/issues, the following filter is built by selecting the label "activerecord":
+
+`is:issue label:activerecord`
+
+But, you can also find all issues that are NOT labeled activerecord:
+
+`is:issue -label:activerecord`
+
+Additionally, this also works for pull requests:
+
+`is:pr -label:activerecord`
+
+[*Read more about searching issues.*](https://help.github.com/articles/searching-issues)
+
+### Merged pull requests filter
+
+Github has tabs for displaying open or closed issues and pull requests but you
+can also see merged pull requests.  Just put the following in the filter:
+
+`is:merged`
+
+[*Read more about searching issues.*](https://help.github.com/articles/searching-issues)
+
 ### Syntax Highlighting in Markdown Files
 For example, to syntax highlight Ruby code in your Markdown files write: