Reset combo and readme correction

[LeftEmpty]

I wasn't sure whether to post this here or on github, so tell me if I should move it.

I went through the Readme and I've noticed the reset description is a bit erronenous:

Tap the Start + Select buttons together quickly to reset. The PC Engine/Turbografx-16 did not have a hardware reset button, and instead relies on this button combination. The timing needs to be exact to trigger this, and sometimes it will take a couple tries. With this method, in-game options will remain if you have changed them, whereas the MiSTer OSD reset will revert them.

The reset manoeuvre is actually much more simple: you need to have the button Start held down; any subsequent press on the Select button should then reset the machine. Some rare games require you to hold down the Select button a bit longer instead of triggering it near immediately.

Select then Start won't trigger it.

Also there is no mention that the PC Engine mouse is emulated, while it indeed is (and perfectly) ;D

[Sorgelig]

I've updated readme about reset. Mouse was there originally.