Squashed 'lib/mbedtls/external/mbedtls/' content from commit 2ca6c285a0dd

git-subtree-dir: lib/mbedtls/external/mbedtls
git-subtree-split: 2ca6c285a0dd3f33982dd57299012dacab1ff206

.github/pull_request_template.md

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+## Description
+
+Please write a few sentences describing the overall goals of the pull request's commits.
+
+
+
+## PR checklist
+
+Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")
+
+- [ ] **changelog** provided, or not required
+- [ ] **backport** done, or not required
+- [ ] **tests** provided, or not required
+
+
+
+## Notes for the submitter
+
+Please refer to the [contributing guidelines](https://github.com/Mbed-TLS/mbedtls/blob/development/CONTRIBUTING.md), especially the
+checklist for PR contributors.
+
+Help make review efficient:
+* Multiple simple commits
+  - please structure your PR into a series of small commits, each of which does one thing
+* Avoid force-push
+  - please do not force-push to update your PR - just add new commit(s)
+* See our [Guidelines for Contributors](https://mbed-tls.readthedocs.io/en/latest/reviews/review-for-contributors/) for more details about the review process.