Add Gridwright Studio to Assets/Placeholders (#497)

Claude-Session: https://claude.ai/code/session_01PSRseJQhDFiinh9ZASP2ng

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -76,6 +76,7 @@ _Great graphics placeholders and tools to turn that squared game into a picasso
 - :free: [Crisp Icons Free](https://anipixels.itch.io/crisp-icons-free) - 42 rounded game UI icons in white and dark, as 64 px PNG and SVG; royalty-free for commercial use, no credit required. Drawn procedurally by code written with an AI assistant, no image generators.
 - :money_with_wings: [GameDev Market](https://www.gamedevmarket.net/) - a community-driven marketplace that connects indie game developers with talented asset creators.
 - :free: [Games-Icons Set](https://game-icons.net/) - free icons for your games.
+- :money_with_wings: [Gridwright Studio](https://gridwright.store/) - Subscription library of pixel-art game asset packs (tilesets, characters, UI, icons, effects, isometric, music and SFX) for any engine, many with Godot scenes and Tiled tilesets. Free samples with a free account. Drawn in code with AI-assisted tools.
 - :free: [Iconmonstr](https://iconmonstr.com/) - Another free icons resource for your games.
 - :money_with_wings: [Kenney Assets](https://kenney.nl/assets) - Royalty free assets
 - :free: [Liberated Pixel Cup assets](https://lpc.opengameart.org) - Free graphic assets of the Liberated Pixel Cup (LPC) held by the OpenGameArt forums