Add CLI

Closes #12

README.md

@@ -15,7 +15,7 @@ CI server isn't properly detected :)
 npm install is-ci --save
 ```
 
-## Usage
+## Programmatic Usage
 
 ```js
 const isCI = require('is-ci')
@@ -25,6 +25,21 @@ if (isCI) {
 }
 ```
 
+## CLI Usage
+
+For CLI usage you need to have the `is-ci` executable in your `PATH`.
+There's a few ways to do that:
+
+- Either install the module globally using `npm install is-ci -g`
+- Or add the module as a dependency to your app in which case it can be
+  used inside your package.json scripts as is
+- Or provide the full path to the executable, e.g.
+  `./node_modules/.bin/is-ci`
+
+```
+is-ci && echo "This is a CI server"
+```
+
 ## Supported CI tools
 
 Officially supported CI servers:

bin.js

@@ -0,0 +1,4 @@
+#!/usr/bin/env node
+'use strict'
+
+process.exit(require('./') ? 0 : 1)

package.json

@@ -2,6 +2,7 @@
   "name": "is-ci",
   "version": "1.0.10",
   "description": "Detect if your code is running on a CI server",
+  "bin": "bin.js",
   "main": "index.js",
   "dependencies": {
     "ci-info": "^1.0.0"