Add manifest.json for Espressif registry upload

Author: gin66

manifest.json

@@ -0,0 +1,9 @@
+{
+  "version": "1.2.5",
+  "description": "A high speed stepper library for Atmega 168/168p/328/328p (nano), 32u4 (leonardo), 2560, ESP32, ESP32S2, ESP32S3, ESP32C3, ESP32C6, Atmel SAM Due, Raspberry pi pico and pico 2",
+  "documentation": "https://github.com/gin66/FastAccelStepper",
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/gin66/FastAccelStepper.git"
+  }
+}