Create PULL_REQUEST_TEMPLATE.md

Author: trnxdev

.github/PULL_REQUEST_TEMPLATE.md

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+### What does this pull request do?
+- [ ] Bug fix
+- [ ] Refractor
+- [ ] Custom <!-- Please specify -->
+
+<!-- https://github.com/ytdl-org/youtube-dl/blob/master/.github/PULL_REQUEST_TEMPLATE.md?plain=1 -->
+### In order to be merged, each piece of this code must be released under public domain or under the [Unilicense](http://unlicense.org/). Check one of the following options:
+
+- [ ] I am the original author of this code and I am willing to release it under Unlicense
+- [ ] I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)