chore(docs): Added contribution templates, SECURITY policy

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,2 +1,33 @@
-Please read the pull request checklist to make sure your changes are merged: https://github.com/frappe/erpnext/wiki/Pull-Request-Checklist
+<!--
 
+Some key notes before you open a PR:
+
+ 1. Select which branch should this PR be merged in?
+ 2. PR name follows [convention](http://karma-runner.github.io/4.0/dev/git-commit-msg.html)
+ 3. All tests pass locally, UI and Unit tests
+ 4. All business logic and validations must be on the server-side
+ 5. Update necessary Documentation
+ 6. Put `closes #XXXX` in your comment to auto-close the issue that your PR fixes
+
+
+Also, if you're new here
+
+- Documentation Guidelines => https://github.com/frappe/erpnext/wiki/Updating-Documentation
+
+- Contribution Guide => https://github.com/frappe/frappe/blob/develop/.github/CONTRIBUTING.md
+
+- Pull Request Checklist => https://github.com/frappe/erpnext/wiki/Pull-Request-Checklist
+
+-->
+
+> Please provide enough information so that others can review your pull request:
+
+<!-- You can skip this if you're fixing a typo or updating existing documentation -->
+
+> Explain the **details** for making this change. What existing problem does the pull request solve?
+
+<!-- Example: When "Adding a function to do X", explain why it is necessary to have a way to do X. -->
+
+> Screenshots/GIFs
+
+<!-- Add images/recordings to better visualize the change: expected/current behviour -->