README: tweak markup, grammar + misc.

I don't know why you want main headers to be smaller? less visible? It is not part of bigger documentation, it is main page.
I guess 18 mm are more visible and available everywhere at the internet and is more proper version? If not the 18mm should be changed in the final reports, as well.
The "You" is intended here. It is more gentle form.
I don't use "Hence" at all, I usually use "so". "Hence" is odd to me, it is not me.
"(pl)" - can be any language with first "p" letter. The "pl" is used in code variables not in documentations or full descriptions, I guess.
Regarding "more". The chipboards can be cut without it, but with this is "more" easier. "More" is intended here, to emphasize that.
This "thickness/size/name/folders" can be done in technical code comments not in human readable descriptions.
"disabling" is also technical world. This can be used in technical documentation, or code comments but rather not at the main page with features descriptions. It is too technical. Main page should be for humans, simple, readable, not technical.
"Please direct" I don't like that, it is more official, more like forcing someone. I want to leave it more gentle, kind. It is not political-corporate code.
All others, I agree. Thanks.

dprojects / getDimensions