Interface to SP7789 based display

[MoskitoAndi]

To interface a ST7789 based display, as per Readme.md I had to do some changes. In st7789.cpp I had to redefine the LCD_PIN definitions to LCD_PIN_DC = GPIO_NUM_2; LCD_PIN_BCKL = GPIO_NUM_15; And I had to connect the RST pin of the display to the RST Pin on T-Beam.

That done, everything works a treat. You might want to change those settings in the correspondig file though. or change the Readme.md Thanks for Your awesome work!