add an intro

CONTRIBUTING.md

@@ -1,5 +1,7 @@
 # Contributing to the GitHub Pages Gem
 
+Hi there! We're glad you're interested in contributing to the GitHub Pages Gem. Before you do, please be sure to read the following:
+
 ## Where to get help or report an issue
 
 ### Bugs

ISSUE_TEMPLATE.md

@@ -1,6 +1,6 @@
 ### Before submitting an issue, please be sure to
 
-- [ ] Read [the contributing instructions](https://github.com/github/pages-gem/blob/master/CONTRIBUTING.md)
+- [ ] Read [the contributing instructions](https://github.com/github/pages-gem/blob/master/CONTRIBUTING.md#contributing-to-the-github-pages-gem)
 - [ ] Update to the latest Gem version (either `gem update pages-gem` or `bundle update pages-gem`)
 
 ### This issue affects