fix typo: correct preposition usage and add missing period in contrib…

[ozzy35410]

…ution guidelines

[cla-assistant]

All committers have signed the CLA.

[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[OlivierBBB]

Hi there @ozzy35410, thank you for your interest in this repo. We do not accept non-code contributions like fixing comments, typos or some other trivial fixes (cf. our guidelines). What would make sense is to open an issue pointing to any of those errors, and we will batch them into a single change.

Cheers