added templates and enhanced readme (#307)

Co-authored-by: Justin Lee <justinai@fb.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,31 @@
+# What does this PR do?
+
+Closes # (issue)
+
+## Feature/Issue validation/testing/test plan
+
+Please describe the tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
+Please also list any relevant details for your test configuration or test plan.
+
+- [ ] Test A
+Logs for Test A
+
+- [ ] Test B
+Logs for Test B
+
+
+## Sources
+
+Please link relevant resources if necessary.
+
+
+## Before submitting
+- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
+- [ ] Did you read the [contributor guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
+      Pull Request section?
+- [ ] Was this discussed/approved via a Github issue? Please add a link
+      to it if that's the case.
+- [ ] Did you make sure to update the documentation with your changes?
+- [ ] Did you write any new necessary tests?
+
+Thanks for contributing 🎉!