updates readme.md

[rladstaetter]

fixes typo; adds a hint to help cmake find Qt

[miho]

Thanks for spotting the typo.

[miho]

I would rather prefer consistent hints for CMake on Windows and Unix. Setting the prefix_path might work in this case but I prefer setting the Qt5_Dir.

Can you try whether setting the Qt5_Dir works for you as well?

Thanks.

[rladstaetter]

i don‘t know why but setting Qt5_Dir didn‘t work for me. 😞

[miho]

Can you let me know your OS and the exact path you entered? Would like to fix this.

[miho]

and pls do a ls in the directory you entered. Then I'll try to reproduce it.

[rladstaetter]

ok, it was a false alarm, my bad, i just provided the wrong directory for 'Qt5_Dir'.

I removed the superfluous entry concerning prefix_path, spotted another typo, added a hint for Qt5_Dir in the readme.md.

also added an entry for ignoring .idea/ in .gitignore.

[rladstaetter]

i could compile nativefx-qt like described in the readme, just by providing the correct Qt5_Dir.

[miho]

Very cool. Thanks! Still would like to know your OS ;-) Linux or Mac?

[rladstaetter]

i've tested NativeFX with macOS Mojave 10.14.5 👍