Add Github PR Convention to PR templates

Author: ffaf1

.github/PULL_REQUEST_TEMPLATE/full_pr.md

@@ -4,7 +4,8 @@ labels: ["attention: needs-review"]
 
 ---
 
-Please include the following checklist in your PR:
+Read [Github PR Conventions](https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#github-pull-request-conventions)
+and please include the following checklist in your PR:
 
 * [ ] Patches conform to the [coding conventions](https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#other-conventions).
 * [ ] Any changes that could be relevant to users [have been recorded in the changelog](https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#changelog).

.github/PULL_REQUEST_TEMPLATE/simple_pr.md

@@ -4,6 +4,7 @@ labels: ["attention: needs-review"]
 
 ---
 
-Please include the following checklist in your PR:
+Read [Github PR Conventions](https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#github-pull-request-conventions)
+and please include the following checklist in your PR:
 
 * [ ] Patches conform to the [coding conventions](https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#other-conventions).