Update HOW_YOU_CAN_HELP.md

[salartarium]

Summary

Bugfixes "Fix typo"

Purpose of change

In the how to contribute section the word "and" is accidently repeated twice. This is a grammatical error.

Describe the solution

Delete the repeated word, so there is only one and.

Describe alternatives you've considered

I have considered rewriting the whole section, but I am not a regular CDDA contributor nor an intelligent writer.

Testing

I proofread the resulting sentence and used GitHub's automated testing.

Additional context

This document could be heavily revised for both utility and style.