update docs

README.md

@@ -21,16 +21,23 @@ const getPromise = require('native-or-another')
 ```
 
 ### [nativeOrAnother](./index.js#L44)
-> Always will expose native `Promise` if available. Otherwise given promise module or Bluebird.
+> Always will expose native `Promise` if available. Otherwise given promise module or Bluebird if installed, otherwise throws with message.
 
-- `[Prome]` **{Function}** custom promise module    
-- `returns` **{Function}** native Promise or another  
+- `[Promize]` **{Function}** custom promise module    
+- `returns` **{Function}** native Promise or another
+- `throws` **{Error}** possible when
+  1. no native Promise support and
+  2. no `Promize` implementation (constructor) were given and
+  3. no `bluebird` not installed (as devDependency is enough)
 
 **Example**
 
 ```js
 const fs = require('fs')
 const NativeOrBluebird = getPromise()
+// => `bluebird` promise, but only if installed,
+// throws otherwise
+
 const NativeOrPromise = getPromise(require('promise'))
 const NativeOrPinkie = getPromise(require('pinkie'))
 const NativeOrQ = getPromise(require('q'))

index.js

@@ -11,7 +11,8 @@ var NativePromise = require('native-promise')
 
 /**
  * Always will expose native `Promise` if available.
- * Otherwise given promise module or Bluebird.
+ * Otherwise given promise module or Bluebird if installed,
+ * otherwise throws with message.
  *
  * **Example**
  *
@@ -42,6 +43,11 @@ var NativePromise = require('native-promise')
  * @name   nativeOrAnother
  * @param  {Function} `[Promize]` custom promise module
  * @return {Function} native Promise or another
+ * @throws {Error} If
+ *     1. no native Promise support AND
+ *     2. no `Promize` implementation (constructor) were given AND
+ *     3. no `bluebird` were not found/installed (as devDependency is enough)
+ *
  * @api public
  */
 module.exports = function nativeOrAnother (Promize) {