Mention CONTRIBUTING.md to be part of the repo itself

Author: holtowd

.github/ISSUE_TEMPLATE/bug_report.md

@@ -18,6 +18,7 @@ This repository is responsible for the following files
 * CMakeLists.txt
 * tests/*
 * CODE_OF_CONDUCT.md
+* CONTRIBUTING.md
 * LICENSE.txt
 * README.md
 * Non-API headers

.github/pull_request_template.md

@@ -9,6 +9,7 @@ This repository is responsible for the following files
 * CMakeLists.txt
 * tests/*
 * CODE_OF_CONDUCT.md
+* CONTRIBUTING.md
 * LICENSE.txt
 * README.md
 * Non-API headers

CONTRIBUTING.md

@@ -17,6 +17,7 @@ The majority for the Vulkan headers come from [Vulkan-Docs](https://github.com/K
 * CMakeLists.txt
 * tests/*
 * CODE_OF_CONDUCT.md
+* CONTRIBUTING.md
 * LICENSE.txt
 * README.md
 * Non-API headers