Added qt-assistant-compat package.

Hello i added the qt-assistant-compat package. 

Homebrew usually handles the symlinking of things from ``` {bin} ```, ``` {include} ``` and ``` {lib} ``` automatically. It doesn't often need it specified. Theoretically, as long as the ``` #{lib}/QtAssistant.framework ``` is being installed in ``` {lib} ``` then it'll automatically symlink into ``` {homebrewprefix}/lib ```. I'll leave the final word down to Mike here, but I'm not sure the manual symlinking is required.