docs: update docs

Author: aprilandjan

README.md

@@ -1,12 +1,80 @@
 # check-npm-client
 
-This module helps to ensure using of [npm](https://github.com/npm/cli) or [yarn](https://github.com/yarnpkg/yarn) as npm client before try to install any dependencies to your project. It is currently working in progress.
+`npm` and `yarn` are both npm clients used to manage node.js project dependencies. They are somehow different in some behavior, and thus can affect project running.
 
-## references
+This package provide ready-to-use functionality to check current npm client. When used as [pre](https://docs.npmjs.com/misc/scripts#hook-scripts) commands in npm scripts, it will check if the script is executed by specific npm client (`yarn` or `npm`). If it is restricted, then the script execution will be aborted early.
+
+## Usage Scenario
+
+`yarn` uses [yarn.lock](https://yarnpkg.com/lang/en/docs/yarn-lock/) to ensure versions of dependencies, but `npm` use [package-lock.json](https://docs.npmjs.com/files/package-lock.json) to do that instead. If you use `yarn` to install dependencies in a project which is actually managed by `npm` and `package-lock.json`, the actually installed dependencies in `node_modules` might be different due to [semver](https://docs.npmjs.com/misc/semver) behavior, and this could lead to some un-expected exception while code running.
+
+This is common when working with others because people tends to use `yarn` or `npm` as their wishes.
+
+## Installation
+
+```bash
+$ npm install check-npm-client
+```
+
+or alternatively, with `yarn`:
+
+```bash
+$ yarn add check-npm-client
+```
+
+## Example
+
+This package provide a command line tool to invoke checking functionality:
+
+```bash
+# the user must use `npm` to execute the script
+$ check-npm-client --npm-only
+
+# the user must use `yarn` to execute the script
+$ check-npm-client --yarn-only
+
+# automatically check according to current working directory lock files if exists
+# not available yet
+$ check-npm-client
+```
+
+Besides, you can use it programmatically:
+
+```javascript
+const { checkNpmClient } = require('check-npm-client');
+console.log(checkNpmClient('yarn'));  // true/false
+```
+
+### Ensure before installation
+
+Add the script in your `package.json` to ensure that user must install dependencies with `yarn`:
+
+```json
+{
+  "scripts": {
+    "preinstall": "check-npm-client --yarn-only"
+  }
+}
+```
+
+**Note**: `yarn` and `npm` treat `preinstall` script a little differently. `npm` execute it only before `npm install` (not before `npm install <module>`), but `yarn` always run it before any installation. See [issue](https://github.com/npm/cli/issues/481) here. So if specified as `--yarn-only` and user use `npm` to install another dependency, the `preinstall` will not be invoked (so the ensurance will fail).
+
+### Ensure before any other script
+
+Add the script in your `package.json` to ensure that user must use `npm` to run the script `my-task`:
+
+```json
+{
+  "scripts": {
+    "premy-task": "check-npm-client --npm-only",
+    "my-task": "node my-task.js"
+  }
+}
+```
+
+## References
 
-- <https://github.com/nodejs/node/issues/14957>
-- <https://github.com/yibn2008/find-process>
-- <https://github.com/timoxley/npm-which>
 - <https://github.com/npm/cli/issues/481>
+- <https://github.com/yibn2008/find-process>
 - <https://stackoverflow.com/questions/46725374/how-to-run-a-script-before-installing-any-npm-module>
 - <https://github.com/yarnpkg/yarn/issues/5063>

bin/cli.js

@@ -1,7 +1,7 @@
 #!/usr/bin/env node
 
 const chalk = require('chalk');
-const { debug, ensureNpm, ensureYarn } = require('../lib/utils');
+const { debug, ensureNpm, ensureYarn } = require('../lib');
 
 const helpText = `
 ${chalk.green('Usage')}

lib/check-npm.js

@@ -1,20 +1,27 @@
 {
   "name": "check-npm-client",
+  "description": "A utility to check which npm client(yarn/npm) is used",
   "version": "1.0.0",
   "author": "aprilandjan",
   "license": "MIT",
   "files": [
-    "bin"
+    "bin",
+    "lib"
   ],
   "engines": {
     "node": ">=7.6.0"
   },
   "bin": {
     "check-npm-client": "./bin/cli.js"
   },
+  "main": "./lib/index.js",
   "scripts": {
     "check": "node check.js"
   },
+  "repository": {
+		"type": "git",
+		"url": "https://github.com/aprilandjan/ascii-tree-generator"
+	},
   "dependencies": {
     "chalk": "^3.0.0",
     "debug": "^4.1.1",