Add a notice about broken commands

[nikitaeverywhere]

Because of some core blockers like #92 and WebTerminal's implementation basing on WebSockets, terminal commands for debugging and some of those:

• PRINT – Displays lines of code from the current routine on the current device.
• ZINSERT – Inserts one or more lines of code into the current routine.
• ZLOAD – Loads a routine into the current routine buffer.
• ZPRINT – Displays lines of code from the current routine on the current device.
• ZREMOVE – Deletes a line or a range of lines from the current routine, or unloads the current routine.
• ZSAVE – Saves the current routine.
• ZZPRINT – Displays one or more source code lines from a routine

may not work properly. The WebTerminal UI should warn about it. Reference.