Documentation improvements

[The documentation](https://19majkel94.github.io/type-graphql) was written a bit carelessly because that time I was focusing on iterating with code and features. Also my English is rather on B2/C1 level. That's why there might be some typos and grammar mistakes 😞

So I would like to ask the community to get involved in this project and help making TypeGraphQL great ~again~ at least 😄 If you found a typo or other mistake in docs, feel free to report it or even create a PR with fix for that!

Also, there are some voice that some design goals and architectural choices that I've made are a bit non-intuitive:
> sometimes, it's good to have documentation being written by someone else or at least being updated by a person who is not an author of the library and don't have full knowledge about why given design decision have been made

So if you find something like that - also feel free to report that. I will try to clarify it and improve the docs or maybe it might be a good point for a new feature?

Thank you, guys!
Let's contribute and celebrate [Hacktoberfest](https://hacktoberfest.digitalocean.com/)! 🎉

Start with the linked TypeGraphQL documentation and look for a specific typo, grammar mistake, or unclear explanation of a design choice. Choose one documented problem, report it or prepare a focused documentation change, and confirm that the revised text is clearer and accurate.

Written by the indexing model from the issue text.