Created a template for pull requests

Author: yash

.github/pull_request_template.md

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+<!-- Please follow this checklist and put an x in each of the boxes, like this: [x]. It will ensure that our team takes your pull request seriously. -->
+
+- [ ] My pull request has a descriptive title (not a vague title like `Update index.md`)
+- [ ] My pull request targets the `master` branch of creativecommons.github.io-source.
+
+<!-- If your pull request closes a GitHub issue, replace the XXXXX below with the issue number. -->
+
+Closes #XXXXX
+
+<!-- You may add your description of the pull request underneath this line. -->