Offer hints on entering APL symbols to first-time users

[mkromberg]

Offer first-time users hints on how to enter APL characters (with a "don't remind me again" option). This suggestion came up during a presentation of Ride to non-Dyalog users at Minnowbrook.

[MaxCan-Code]

Instructions available in https://mastering.dyalog.com/Getting-Started.html#auto-complete