Adding instructions to the Code Review agent (#31)

Following the guide from https://docs.github.com/en/copilot/how-tos/agents/copilot-code-review/using-copilot-code-review\#customizing-copilots-reviews-with-custom-instructions

Author: aaronpowell

.github/copilot-instructions.md

@@ -0,0 +1,7 @@
+When performing a code review, validate that there are changes in the `README.md` file that match the changes in the pull request. If there are no changes, or if the changes do not match, then the pull request is not ready to be merged.
+
+When performing a code review, ensure that the values in the front matter are wrapped in single quotes.
+
+When performing a code review, ensure that the `description` field in the front matter is not empty.
+
+When performing a code review on a `.instructions.md` file, ensure there is an `applyTo` property in the front matter that specifies the file or files to which the instructions apply.