Minor README fix (#6098)
Minor README fix (#6098)

Fix Linux location typos (lowercase "arduino" and missing "/").

Fixes #6093
sticilface/Arduino,sticilface/Arduino,esp8266/Arduino,esp8266/Arduino,sticilface/Arduino,esp8266/Arduino,esp8266/Arduino,esp8266/Arduino,sticilface/Arduino,sticilface/Arduino