Fix grammatical mistakes

### Is your feature request related to a problem? Please describe.

Fix grammatical mistakes under [this](https://github.com/anitab-org/documentation/blob/master/ways-to-contribute.md#ways-to-contribute) section.

### Example

This document lists the many ways you as a member of this community can contribute to our community! You can be a newcomer to the community or someone who is with us for a while :)