adding font readme

fonts/README.md

@@ -1,3 +1,14 @@
 # Fonts
 
-`inter_20.bin`: 20px 4 bpp font
+Generated with https://lvgl.io/tools/fontconverter
+
+`inter_20.bin`: 20px 4 bpp font
+
+Adding a custom font to the binary:
+
+highlevel
+- Create `lv_font_my_26.c` using tool above
+- add font to lvgl/src/font
+- update lvgl.h with  `#define LV_FONT_CUSTOM_DECLARE LV_FONT_DECLARE(lv_font_my_26)`
+- Build and import using `lv.font_my_26`
+