.github/*: point to Homebrew Evolution repository. (#259)

Indicate that feature requests should go there rather than here.

.github/CONTRIBUTING.md

@@ -8,4 +8,8 @@ First time contributing to Homebrew? Read our [Code of Conduct](https://github.c
 * read [the Troubleshooting Checklist](https://github.com/Homebrew/brew/blob/master/share/doc/homebrew/Troubleshooting.md#troubleshooting)
 * open an issue on the formula's repository
 
+### Propose a feature
+
+* Please create a pull request with your change proposal in the [Homebrew Evolution](https://github.com/Homebrew/brew-evolution) repository using the [proposal template](https://github.com/Homebrew/brew-evolution/blob/master/proposal_template.md).
+
 Thanks!

.github/ISSUE_TEMPLATE.md

@@ -10,8 +10,6 @@ _You can erase any parts of this template not applicable to your Issue._
 
 Please replace this line with a brief summary of your issue.
 
-### Feature Requests:
+### Propose a feature:
 
-**Please note by far the quickest way to get a new feature into Homebrew is to file a [Pull Request](https://github.com/Homebrew/brew/blob/master/.github/CONTRIBUTING.md).**
-
-We will consider your request but it may be closed if it's something we're not actively planning to work on.
+Instead of creating an issue here, please create a pull request with your change proposal in the [Homebrew Evolution](https://github.com/Homebrew/brew-evolution) repository using the [proposal template](https://github.com/Homebrew/brew-evolution/blob/master/proposal_template.md).