Add more roadmap notes to README

Author: PaintYourDragon

README.md

@@ -36,6 +36,8 @@ The PRIME DIRECTIVE is to maintain backward compatibility with existing Arduino
 
 - Additional or incompatible bitmap formats, for similar reasons. It's getting messy.
 
+- Adding background color to custom fonts to erase prior screen contents. The ONLY acceptable methods are to clear the area with a filled rect, or (to avoid flicker) draw text into a GFXcanvas1 and copy to screen with drawBitmap() w/background color. This is on purpose and by design. We've discussed this. Glyphs can overlap.
+
 - Scrolling, whether hardware- or software-based. Such implementations tend to rely on hardware-specific features (not universally available), read access to the screen's framebuffer (ditto) and/or the addition of virtual functions in GFX which them must be added in *every* subclass, of which there are many. The GFX API is largely "set" at this point and this is just a limitation we live with now.
 
 - Please don't reformat code for the sake of reformatting code. The resulting large "visual diff" makes it impossible to untangle actual bug fixes from merely rearranged lines. clang-format will be the final arbiter.