Building Readme

[BestVanRome]

Just in case you want to update your building hints for Linux:

A student of mine was Building on WSL2 and commented that he had to do some updates to make it work:
Changes:

• python3-opencv, not available any more.
• wget, old link was "http" (is corrected automatic), but showed on an old not available version. Seem to be that those kind of links will be present not for long, the newest (Qt 5.15) mentions this in a doc there on the site)
• had also to install sudo apt-get install libxkbcommon-x11-0 to make it work (maybe just an WSL2 thing?)

Best regards