README: expand on the textual form of filters

[Artoria2e5]

Add information on groups and evaluation order.

[Querz]

The filters do indeed work from left to right, but they still respect the "AND before OR"-rule.
Using your example A and B or C and D, it actually checks A and B first and if that is true, it skips the rest (that's how it works in most programming languages as far as i know).
Let's assume the following:
A = true, B = true, C = false, D = false.
Now A and B or C and D must return true, because A and B is true and we don't care about C and D, but (((A and B) or C) and D) from your example would return false.

Digging deeper into the actual code that performs those checks, I did find a bug when it tests if the query actually applies to a region file. See the Notice at the end of the Chunk filter section in the Readme.
I fixed this bug here, it will be available in the next release.

[Artoria2e5]

Oops, you are right about the rule thing. I bumped into those sort of evaluation rules in sh, so I was assuming that mcaseelctor did the same.