Update README with run/build instructions

README.md

@@ -4,13 +4,27 @@
 
 Make it easier to re-use and template CloudFormation templates
 
-## Current
+## Functionality
+
+### Current
 
 * Supports serializing/deserializing yaml
 * Can specify an input file; will pull in all referencing files and merge them and write to an output file
 * Supports `!Unset` and `!Replace`
 
-## Planned
+### Planned
 
 * Provision rendered templates directly to CloudFormation
 
+## Usage
+
+### Running
+
+* Install dependencies with `composer install`
+* Execute `cfnpp` with PHP.
+
+### Building
+
+* Install dependencies with `composer install`
+* Run `./cfnpp app:build`; outputs phar at builds/
+