doc: Add updated TFT display config

doc/tft_display.txt

@@ -1,3 +1,11 @@
+Update:
+
+Add to /boot/config.txt:
+dtparam=spi=on
+dtoverlay=adafruit18,rotate=0
+
+Old:
+
 TFT Display
 --
 Driver: https://github.com/notro/fbtft