Expand PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,2 +1,28 @@
-<!-- Make sure you are targeting Microsoft/react-native for your PR, if you mean to submit your change to the Microsoft fork, instead of to Facebook's react-native -->
+# :warning: Make sure you are targeting Microsoft/react-native for your PR :warning:
+(then delete these lines)
+
+<!--
+We are working on reducing the diff between Facebook's public version of react-native, and our Microsoft/react-native.  Long term, we want to remove the need for our version and only depend on Facebook's react-native.  In order to move in the right direction, new changes should be examined to ensure that we are doing the right thing.
+
+If you are making a new change then one of the following should be done:
+- Consider if it is possible to achieve the desired behavior without making a change to react-native.  Often a change can be made in a layer above react-native instead.
+- Create a corresponding PR against [react-native on GitHub](https://github.com/facebook/react-native)
+**Note:** Ideally you would wait for GitHub feedback before submitting to ISS, since we want to ensure that ISS doesn't deviate from GitHub.
+-->
+
+#### Please select one of the following
+- [ ] I am removing an existing difference between facebook/react-native and Microsoft/react-native :thumbsup:
+- [ ] I am cherry-picking a change from Facebook's react-native into Microsoft/react-native :thumbsup:
+- [ ] I am making a fix / change for the macOS implementation of react-native
+- [ ] I am making a change required for Microsoft usage of react-native
+
+#### Description of changes
+
+(give an overview)
+
+#### Focus areas to test
+
+(optional)
+
+