docs(only-allow-pnpm): added option to enforce pnpm with package.json and .npmrc

docs/only-allow-pnpm.md

@@ -1,21 +1,67 @@
 ---
 id: only-allow-pnpm
-title: Only allow pnpm
+title: Only Allow PNPM
 ---
 
-When you use pnpm on a project, you don't want others to accidentally run
-`npm install` or `yarn`. To prevent devs from using other package managers,
-you can add the following `preinstall` script to your `package.json`:
+When many developers are working on the same project together, you need a failsafe in case someone accidentally runs commands with another package manager (like NPM, Yarn, or Bun).
 
-```json
+To prevent dependency management conflicts between package managers:
+
+1. Create a file, if it doesn't already exist, named `.npmrc` at the root of your project.
+2. Toggle the following configuration variable in your `.npmrc` on:
+
+```
+engine-strict=true
+```
+
+3. Specify the following fields in your `package.json`:
+
+```
 {
-	"scripts": {
-		"preinstall": "npx only-allow pnpm"
-	}
+  "devEngines": {
+    "runtime": {
+      "name": "node",
+      "onFail": "error"
+    },
+    "packageManager": {
+      "name": "pnpm",
+      "version": "10.13.1",
+      "onFail": "error"
+    }
+  },
+  "engines": {
+    "node": ">=18.18.0",
+    "pnpm": ">=10.0.0"
+  },
 }
 ```
 
-Now, whenever someone runs `npm install` or `yarn`, they'll get an
-error instead and installation will not proceed.
+- Now, when you run `npm i`, `npm i -D` (or an equivalent), these commands return this error:
+
+```
+username@hostname some-project % npm i -D package
+npm error code EBADDEVENGINES
+npm error EBADDEVENGINES The developer of this package has specified the following through devEngines
+npm error EBADDEVENGINES Invalid engine "packageManager"
+npm error EBADDEVENGINES Invalid name "pnpm" does not match "npm" for "packageManager"
+npm error EBADDEVENGINES {
+npm error EBADDEVENGINES   current: { name: 'npm', version: '10.0.0' },
+npm error EBADDEVENGINES   required: { name: 'pnpm', onFail: 'error' }
+npm error EBADDEVENGINES }
+npm error A complete log of this run can be found in: /Users/username/.npm/_logs/2021-08-21T00_00_00_000Z-debug-0.log
+```
+
+---
+
+Alternatively, in your `package.json`, you can specify the following `preinstall` script:
+
+```
+{
+  "scripts": {
+    "preinstall": "npx only-allow pnpm"
+  }
+}
+```
 
-If you use npm v7, use `npx -y` instead.
+- You may also install the package `only-allow` as a dev dependency.
+- For NPM version 7+, you may need to run `npx -y only-allow pnpm` instead.