chore: add changeset for btc-assets-api docs

Author: fghdotio

.changeset/modern-bags-marry.md

@@ -0,0 +1,8 @@
+---
+'rgbpp': patch
+---
+
+docs: update btc-assets-api documentation and FAQ
+
+- Update FAQ on accessing btc-assets-api
+- Update API endpoints and fix deprecated links