chore(npm): add engines and nvmrc for easier node version handling

.nvmrc

@@ -0,0 +1 @@
+v16.15.0

CONTRIBUTING.md

@@ -5,9 +5,10 @@ Thank you for considering contributing to Leaflet-Geoman.
 Follow these steps to get up and running:
 
 1.  clone the repository
-2.  run `npm install`
-3.  run `npm start` to compile dev version and use watch mode
-4.  run `npm run cypress` to launch the test suite (also nice for TDD)
-5.  run `npm run test` to run cypress tests
-6.  run `npm run lint` to check the code with eslint
-7.  run `npm run prepare` to compile the build version
+2.  Make sure you run the node version specified in package.json under "engines" or run `nvm use`
+3.  run `npm install`
+4.  run `npm start` to compile dev version and use watch mode
+5.  run `npm run cypress` to launch the test suite (also nice for TDD)
+6.  run `npm run test` to run cypress tests
+7.  run `npm run lint` to check the code with eslint
+8.  run `npm run prepare` to compile the build version

package.json

@@ -18,6 +18,9 @@
   "files": [
     "dist"
   ],
+  "engines": {
+    "node": ">=16.13 <17"
+  },
   "main": "dist/leaflet-geoman.min.js",
   "types": "dist/leaflet-geoman.d.ts",
   "dependencies": {