Contributing chapter needs proof-reading

[miohtama]

The Contributing chapter has some non-native speaker English and might need little love to get all sentences make sense.

[keikoro]

I've already looked at it and clarified and corrected some things in the first half of the file! Need to switch to something else now, will come back to it later... (but feel free to continue where I left off).

[EdgyEdgemond]

Looks like adding a comment marking an issue as fixed doesnt work as well as adding it in the PR comment. This can be closed.

[oinopion]

Done.