Clarify Qt license statements

[johnthagen]

The README states:

Linux wheels ship with Qt 4.8.7 licensed under the LGPLv2.1.
MacOS wheels ship with Qt 5 licensed under the LGPLv3.

And LICENSE-3RD-PARTY.txt state:

https://github.com/skvark/opencv-python/blob/3073e9ee37f016144893deeceb127766f55083dc/LICENSE-3RD-PARTY.txt#L84

https://github.com/skvark/opencv-python/blob/3073e9ee37f016144893deeceb127766f55083dc/LICENSE-3RD-PARTY.txt#L591

I was under the impression that the -headless wheels didn't have Qt in them. Should these statements be adjusted to something like:

"Linux non-headless wheels ship with Qt..."

[skvark]

Yeah, headless versions do not have Qt.

[johnthagen]

@skvark 👍 Fixed in #350