Add mneme to testing section (#4852)

README.md

@@ -1521,6 +1521,7 @@ There are [other sites with curated lists of elixir packages](#other-awesome-lis
 * [mix_test_interactive](https://github.com/influxdata/mix_test_interactive) - Interactive test runner for mix test with watch mode.
 * [mix_test_watch](https://github.com/lpil/mix-test.watch) - Automatically run your Elixir project's tests each time you save a file.
 * [mixunit](https://github.com/talentdeficit/mixunit) - An EUnit task for Mix based projects.
+* [mneme](https://github.com/zachallaun/mneme) - Assertions that know how to update themselves, otherwise known as snapshot or approval testing.
 * [mock](https://github.com/jjh42/mock) - Mocking library for the Elixir language.
 * [mockery](https://github.com/appunite/mockery) - Simple mocking library for asynchronous testing.
 * [mockingbird](https://github.com/Driftrock/mockingbird) - A set of helpers to test code that involves http requests.