doc: add command options to README.md

Documents options accepted by node-gyp.
Continuation of nodejs#880.

Author: gibfahn

README.md

@@ -44,11 +44,11 @@ You will also need to install:
   * On Windows:
     * Visual C++ Build Environment:
       * Option 1: Install [Visual C++ Build Tools](http://go.microsoft.com/fwlink/?LinkId=691126) using the **Default Install** option.
-      
+
       * Option 2: Install [Visual Studio 2015](https://www.visualstudio.com/products/visual-studio-community-vs) (or modify an existing installation) and select *Common Tools for Visual C++* during setup. This also works with the free Community and Express for Desktop editions.
-     
+
       > :bulb: [Windows Vista / 7 only] requires [.NET Framework 4.5.1](http://www.microsoft.com/en-us/download/details.aspx?id=40773)
-    
+
     * Install [Python 2.7](https://www.python.org/downloads/) (`v3.x.x` is not supported), and run `npm config set python python2.7` (or see below for further instructions on specifying the proper Python version and path.)
     * Launch cmd, `npm config set msvs_version 2015`
 
@@ -144,6 +144,7 @@ Commands
 
 | **Command**   | **Description**
 |:--------------|:---------------------------------------------------------------
+| `help`        | Shows the help dialog
 | `build`       | Invokes `make`/`msbuild.exe` and builds the native addon
 | `clean`       | Removes the `build` directory if it exists
 | `configure`   | Generates project build files for the current platform
@@ -153,6 +154,34 @@ Commands
 | `remove`      | Removes the node development header files for the given version
 
 
+Command Options
+--------
+
+`node-gyp` accepts the following command options:
+
+| **Command**                       | **Description**
+|:----------------------------------|:------------------------------------------
+| `-j n`, `--jobs n`                | For `build`: run n parallel builds
+| `--silly`, `--loglevel=silly`     | Log all progress to console
+| `--verbose`, `--loglevel=verbose` | Log most progress to console
+| `--silent`, `--loglevel=silent`   | Don't log anything
+| `--debug`                         | Make Debug build (default=Release)
+| `--release`, `--no-debug`         | Make Release build
+| `--directory=$dir`                | Run command in different directory
+| `--make=$make`                    | Override make command, e.g. with gmake
+| `--thin=$thin`                    | Enable thin static libraries
+| `--arch=$arch`                    | Set target architecture (e.g. ia32)
+| `--tarball=$path`                 | Get headers from a local tarball
+| `--ensure`                        | Don't reinstall headers if already present
+| `--dist-url=$url`                 | Download header tarball from custom URL
+| `--proxy=$url`                    | Set HTTP proxy for downloading header tarball
+| `--cafile=$cafile`                | Override default CA chain (to download tarball)
+| `--nodedir=$path`                 | Set the path to the node binary
+| `--python=$path`                  | Set path to the python (2) binary
+| `--msys_version=$version`         | Set Visual Studio version (win)
+| `--solution=$solution`            | Set Visual Studio Solution version (win)
+
+
 License
 -------