Update docs to mention libuv.

doc/site/getting-started.markdown

@@ -1,8 +1,22 @@
 ^title Getting Started
 
 Getting Wren up and running on your machine should be pretty straightforward.
-Tiny C programs with no dependencies are nice that way. If you're on a Unix or
-Mac and you can rock a command line, it's just:
+Tiny C programs with few dependencies are nice that way. "Wren" encompasses two
+separate artifacts:
+
+ *  **The virtual machine.** This is the core chunk of C that executes Wren
+    source code. It is just a library, not a standalone application. It's
+    designed to be [embedded][] in a larger host application. It has no dependencies beyond the C standard library. You can is use as a static library, shared library, or simply compile the source into your app.
+
+ *  **The command line executable.** Wren also ships with a CLI wrapper around
+    the VM. This gives you a way to run Wren code from the command-line, and
+    also includes modules for talking to the operating system. It depends on
+    [libuv][] for that.
+
+[embedded]: embedding-api.html
+[libuv]: http://libuv.org/
+
+If you're on a Unix or Mac and you can rock a command line, it's just:
 
     :::bash
     $ git clone https://github.com/munificent/wren.git
@@ -10,6 +24,8 @@ Mac and you can rock a command line, it's just:
     $ make
     $ ./wren
 
+This builds both the VM and the CLI. It downloads libuv automatically for you.
+The release build of the CLI goes right into the repo's top level directory.
 Binaries for other configurations are built to `bin/`. Static and shared
 libraries for embedding Wren get built in `lib/`.
 
@@ -18,6 +34,14 @@ Windows brethren, `project/msvc2013` contains a Visual Studio solution. Note
 that these may not have the exact same build settings as the makefile. The
 makefile is the "official" way to compile Wren.
 
+If you only want to build the VM, you can do:
+
+    :::bash
+    $ make vm
+
+This will compile the VM to static and shared libraries. It will not even
+download libuv since it isn't needed.
+
 ## Interactive mode
 
 The above instructions will drop you into Wren's standalone interpreter in