Add Sprite Sheet Builder to Spritesheet Tools (#419)

One new entry in the Graphics > Spritesheet Tools list: a free, browser-only sprite sheet maker (pack frames, split atlases, GIF conversion, PNG + JSON/XML export).

README.md

@@ -92,6 +92,7 @@ _Great graphics placeholders and tools to turn that squared game into a picasso
 - :free: [PixelChart Sprite Sheet Tools](https://pixelchart.app/tools/sprite-sheet-maker/) - Pack frames into a sheet with a JSON atlas, slice sheets back into PNGs, and convert between sheets and animated GIFs. Runs in the browser, no upload.
 - :free: [ShoeBox](http://renderhjs.net/shoebox/) - Adobe Air based app with game and ui related tools.
 - :tada: [SnowB Bitmap Font](https://snowb.org/) - Bitmap font generator
+- :free: [Sprite Sheet Builder](https://spritesheetbuilder.com/) - Free browser-based sprite sheet maker: pack frames, split atlases, convert GIFs, export PNG + JSON/XML for Unity, Godot, Phaser and FNF.
 - :money_with_wings: [TexturePacker](https://www.codeandweb.com/texturepacker) - Great spritesheet creation editor.
 - :tada: [Tilesplit](https://github.com/AlexPoulsen/tilesplit) - CLI text-based tilesheet splitter and namer. Turn a spritesheet into many separate files with names you pick, or not if you don't care. Support templates and textures that are not all the same size.