add motivation

readme.markdown

@@ -20,7 +20,25 @@ The commands are:
 Use "lucifer help [command]" for more information about a command.
 ```
 
+### Why?
+
+Node's `require` is [really, really slow][slow]. If you need to load a large
+app with an unfortunately large number of dependencies to run your test suite,
+you're looking at a 5-10 second penalty to run a single test. 
+
+Instead of requiring every file every time you want to run your test suite,
+load all of them once and listen on a socket for incoming test run requests.
+
+##### But a long running server won't take into account the changes I make
+
+Yes! Luckily it's not too difficult to invalidate the Node cache for a module.
+If you call `lucifer invalidate [file]` the binary will make a request to the
+server to invalidate the cache for that module; this way you can ensure the
+server is running tests against the version of the module on your file system.
+
 ### Install
 
 Run `make install`. You'll want to have Go installed to install the command
 line client.
+
+[slow]: https://kev.inburke.com/kevin/node-require-is-dog-slow/