Fix rendering of Patreon URL in FAQ. Use same "ls" command to find
the serial port that Installation.md uses. Note Raspberry Pi 4 is
supported. Note problems with ModemManager. Point to Bed_Level.md in
Z position_endstop question. Link to Config_checks.md in "Z
screaching" FAQ.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>