Pull request template draft

[ci skip]

.github/pull_request_template.md

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+<!-- This template will help you get your code into PQClean. -->
+
+<!-- Type some lines about your submission -->
+
+
+## Manually checked properties
+<!-- These checkboxes serve for the maintainers of PQClean to verify your submission. Please do not check them yourself. -->
+
+* [ ] `#ifdef`s only for header encapsulation
+* [ ] `api.h` does not include other files
+* [ ] No stringification macros
+* [ ] Output-parameter pointers in functions are on the left
+* [ ] Negative return values on failure of API functions (within restrictions of FO transform).
+* [ ] `const` arguments are labeled as `const`
+* [ ] (optional) All integer types are of fixed size, using `stdint.h` types (including `uint8_t` instead of `unsigned char`)
+* [ ] Integers used for indexing are of size `size_t`
+* [ ] variable declarations at the beginning (except in `for (size_t i=...`)