Add Node.js 16 prerequisite to readme and package.json

package.json

@@ -36,6 +36,9 @@
   ],
   "author": "Junyoung Choi <fluke8259@gmail.com>",
   "license": "GPL-3.0",
+  "engines": {
+    "node": "16.x"
+  },
   "devDependencies": {
     "@babel/core": "^7.6.0",
     "@babel/plugin-proposal-class-properties": "^7.5.5",

readme.md

@@ -41,6 +41,15 @@ Standalone app separated from Boost Note for better local space support. See [Ro
 - `electron` : Compiled electron resources from `npm run build:electron` script. You can run it by `npm start` script. The resources are for packaging the electron app.
 - `src` : Source code.
 
+### Prerequisites
+
+- Node.js 16.x — newer versions are not supported
+
+```sh
+nvm install 16
+nvm use 16
+```
+
 ### Build
 
 Please copy `.env.default` file and create a file named `.env` in the root of the project directory, or the build will fail.
@@ -49,7 +58,7 @@ Please copy `.env.default` file and create a file named `.env` in the root of th
 
 ```sh
 # Install dependencies
-npm i
+npm install
 
 # Run webpack
 npm run dev:webpack