Adding instructions for build utilities.

bin/README.md

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+# Build Utilities
+
+This directory contains utilities used for building OpenLayers applications, 
+generating the API docs, and building hosted versions of the library.
+
+## Dependencies
+
+OpenLayers is built using [Closure Compiler][closure].  The [plovr][plovr] build
+tool simplifies building with Closure Compiler and comes with a built-in version
+of the Closure Library and Compiler.  Both the Compiler and plovr require Java
+version 1.6 or above.  This directory includes a bash/batch script for driving
+plovr.  For pulling down plovr and accessing it in a cross-platform way,
+[Ant][ant] is used.
+
+The instructions below assume that you have added the `ol` bash/batch script to
+your path (type `ol` and see usage docs to confirm this is set up).
+
+[closure]: https://developers.google.com/closure/compiler/
+[plovr]: http://plovr.com/
+[ant]: http://ant.apache.org/
+
+## Building an Application
+
+To compile an application together with OpenLayers, you will provide a build
+configuration file for the compiler.  See the `demo` folder for example 
+configuration files (e.g. `map.json`).
+
+Compile your application with the `build` command:
+
+    ol build path/to/config.json
+
+Substitute the path to your build configuration file above.
+
+## Building the API Docs
+
+From within the root of the OpenLayers directory, use the `doc` command to build
+the API docs:
+
+    ol doc
+
+This will generate documentation in the `jsdoc` directory.
+
+## Building the Hosted Library
+
+To compile the full OpenLayers api, use the `build` command from the root of the
+OpenLayers directory:
+
+    ol build
+
+This will generate an `api.js` script in the same directory.  (This is equivalent to `ol build path/to/ol/api.json`.)
+