Adds lots of Mojo documentation

mojo/edk/embedder/README.md

-# Mojo Embedder Development Kit (EDK)
+# ![Mojo Graphic](https://goo.gl/6CdlbH) Mojo Embedder Development Kit (EDK)
+This document is a subset of the [Mojo documentation](/mojo).
+
+[TOC]
+
+## Overview
 
 The Mojo EDK is a (binary-unstable) API which enables a process to use Mojo both
 internally and for IPC to other Mojo-embedding processes.
 
 Using any of the API surface in `//mojo/edk/embedder` requires (somewhat
 confusingly) a direct dependency on the GN `//mojo/edk/system` target. Despite
 this fact, you should never reference any of the headers in `mojo/edk/system`
 directly, as everything there is considered to be an internal detail of the EDK.
 
+**NOTE:** Unless you are introducing a new binary entry point into the system
+(*e.g.,* a new executable with a new `main()` definition), you probably don't
+need to know anything about the EDK API. Most processes defined in the Chrome
+repo today already fully initialize the EDK so that Mojo's other public APIs
+"just work" out of the box.
+
 ## Basic Initialization
 
 In order to use Mojo in a given process, it's necessary to call
 `mojo::edk::Init` exactly once:
 
 ```
 #include "mojo/edk/embedder/embedder.h"
 
 int main(int argc, char** argv) {
   mojo::edk::Init();
@@ skipping 292 matching lines @@
 module local.mojom;
 
 interface Foo {
   DoSomeStuff(int32 n);
 };
 ```
 
 Once you've bootstrapped your process connection with a real mojom interface,
 you can avoid any further mucking around with EDK APIs or raw message pipe
 handles, as everything beyond this point - including the passing of other
-interface pipes - can be handled eloquently using public bindings APIs.
+interface pipes - can be handled eloquently using
+[public bindings APIs](/mojo#High-Level-Bindings-APIs).
 
-See [additional Mojo documentation](
-    https://www.chromium.org/developers/design-documents/mojo) for more
-information.
+## Setting System Properties
+
+The public Mojo C System API exposes a
+[**`MojoGetProperty`**](/mojo/public/c/system#MojoGetProperty) function for
+querying global, embedder-defined property values. These can be set by calling:
+
+```
+mojo::edk::SetProperty(MojoPropertyType type, const void* value)
+```
+