Expand FAQ and USAGE

FAQ.md

@@ -6,6 +6,10 @@ in JavaScript. It exposes multiple interfaces for users:
 * with `npm i -g documentation`, it provides a binary for command-line usage
 * install `documentation` with `npm` to use the node-facing interace
 
+`documentation` runs in [node.js](https://nodejs.org/) but supports JavaScript
+that runs in _any environment_: you can use it to document browser libraries,
+server libraries, or even things that use RequireJS or other module systems.
+
 ## How does `documentation` differ from JSDoc?
 
 JSDoc is both a **standard syntax for documentating code** as well as a

USAGE.md

@@ -0,0 +1,24 @@
+## Using `documentation` on the command line
+
+Install the `documentation` binary with [npm](https://www.npmjs.com/).
+
+```sh
+$ npm install -g documentation
+```
+
+`documentation` then installs a command called `documentation`. Run it with
+`-h` to get help.
+
+```sh
+$ documentation -h
+Usage: bin/documentation.js <command> [options]
+
+Options:
+  -f, --format   output format, of [json, md]                  [default: "json"]
+  --mdtemplate   markdown template: should be a file with Handlebars syntax
+  -p, --private  generate documentation tagged as private
+  -h, --help     Show help
+
+Examples:
+  documentation foo.js    parse documentation in a given file
+```