Add pull request template and release notes

[nick-harder]

-adds a pull request template for future commits -adds release notes to the documentation

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.20%. Comparing base (70547e6) to head (f935a6e).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #384 +/- ## ======================================= Coverage 78.20% 78.20% ======================================= Files 44 44 Lines 5179 5179 ======================================= Hits 4050 4050 Misses 1129 1129 ``` | [Flag](https://app.codecov.io/gh/assume-framework/assume/pull/384/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=assume-framework) | Coverage Δ | | |---|---|---| | [pytest](https://app.codecov.io/gh/assume-framework/assume/pull/384/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=assume-framework) | `78.20% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=assume-framework#carryforward-flags-in-the-pull-request-comment) to find out more.

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[nick-harder]

Why is it needed to have a separate release_notes.rst instead of linking to https://github.com/assume-framework/assume/releases ?

it is a little bit difficult to maintain the changelog and have the info for the releases. It would be best if people can maintain it with each commit and we can copy paster it during next release