Readme update to make need for pdfium_is_standalone clear.

README.md

 # PDFium
 
 ## News
 
 As of 2016-05-04, GN is used to generate build files replacing GYP. GYP
 support will remain until it is disabled in Chromium and then will be removed
 from PDFium.
 
 As of 2016-04-28, the Visual Studio toolchain from depot_tools is used as the
 default Windows toolchain for Googlers. Please set DEPOT_TOOLS_WIN_TOOLCHAIN=0
 if you need to use the system toolchain. See
 [Windows development subsection](#WinDev) for details.
 
 
 ## Prerequisites
 
 Get the chromium depot tools via the instructions at
 http://www.chromium.org/developers/how-tos/install-depot-tools (this provides
-the gclient utilty needed below).
+the gclient utility needed below).
 
 Also install Python, Subversion, and Git and make sure they're in your path.
 
 
 ###<a name="WinDev"></a> Windows development
 
 PDFium uses a similar Windows toolchain as Chromium:
 
 #### Open source contributors
 Visual Studio 2015 Update 2 or later is highly recommended.
@@ skipping 39 matching lines @@
 We use GN to generate the build files and
 [Ninja](http://martine.github.io/ninja/) (also included with the depot\_tools
 checkout) to execute the build files.
 
 ```
 gn gen <directory>
 ```
 
 If you want to set <directory> to `out/Debug` or `out/Release` you'll need to
 export `GYP_PDFIUM_NO_ACTION=1` to stop `gclient sync` from executing GYP
-and overwritting your build files.
+and overwriting your build files.
 
 ###<a name="BuildConfig"></a> Selecting build configuration
 
 PDFium may be built either with or without JavaScript support, and with
 or without XFA forms support.  Both of these features are enabled by
 default. Also note that the XFA feature requires JavaScript.
 
 Configuration is done by executing `gn args <directory>` to configure the build.
-This will lauch an editor in which you can set the following arguments.
+This will launch an editor in which you can set the following arguments.
 
 ```
 use_goma = true  # Googlers only.
 is_debug = true  # Enable debugging features.
 
 pdf_use_skia = false  # Set true to enable experimental skia backend.
 
 pdf_enable_xfa = true # Set false to remove XFA support (implies JS support).
 pdf_enable_v8 = true  # Set false to remove Javascript support.
 pdf_is_standalone = true  # Set for a non-embedded build.

[Tom Sepez, 2016/05/16 16:07:59]

should this say "Set false for a non-embedded build."

[dsinclair, 2016/05/16 18:40:29]

I don't think so, we want this true if we aren't embedded. It should be false
(the default) for an embedded build.

 
 clang_use_chrome_plugins = false  # Currently must be false.
 ```
 
+Note, you must set `pdf_is_standalone = true` if you want the sample
+applications like `pdfium_test` to build.
+
 When complete the arguments will be stored in `<directory>/args.gn`.
 
 ## Building the code
 
 If you used Ninja, you can build the sample program by:
 `ninja -C <directory>/pdfium_test` You can build the entire product (which
 includes a few unit tests) by: `ninja -C <directory>`.
 
 
 ## Running the sample program
@@ skipping 42 matching lines @@
 and add the "Cr-Internals-Plugins-PDF" label.
 
 ## Contributing code
 
 For contributing code, we will follow
 [Chromium's process](http://dev.chromium.org/developers/contributing-code)
 as much as possible. The main exceptions is:
 
 1. Code has to conform to the existing style and not Chromium/Google style.