Update README.md

[arjendekorte]

Using cmake-presets version 3 requires CMake >= 3.21

[farindk]

Thanks. Could we change the text slightly to "--preset argument needs CMake >= 3.21" ?
Otherwise it sounds to me as it cannot be built without 3.21 at all.

[arjendekorte]

Agreed. It took me a while to figure out what the problem was, since the CMake error isn't the most helpful to find what is wrong, therefor it might be useful to mention this specifically.

[farindk]

Thanks