[WIP] Fix some grammar and typos

[basxto]

There is more. A bunch of sentences feel too nested for English. I only played the first tutorial so far.

Maybe you need to think about how you want to address units.
I’ve got the feeling that you call it “Infantry unit”, but still visualize it as units. That leads to using plural verbs with a singular subject. They are more squads, but in such games the distinction is always blurry.

[czlowiekimadlo]

Thanks for the help! I'm not a native English speaker, so any fix is appreciated!

Indeed, infantry is meant to be squads, but sometimes are treated as individuals, for story reasons. It is indeed blurry. But I think "Infantry unit", while singular, still means multiple people, just organized in a single group, so it makes sense to visualize multiple soldiers?

I did ask an English language specialist for a quota on proofreading these texts, but have not heard from him yet. Maybe I have to poke him :)

So far, these changes look great! Since you have marked this PR as WIP, please let me know if you would like me to merge what is already there, or should I wait for more commits?