Expand the README.

README.md

@@ -9,4 +9,32 @@ This is an experiment for building a Language Server for Scala, in Scala.
 - scala: A Typescript-based Scala extension (language client). Ideally it will be ported to Scala.js
 - ensime-server: An implementation of the Language Server based on Ensime
 
-The language server may be backed up by [ensime](http://ensime.github.io/) or directly by the presentation compiler. Ideally, the language server ca be used as a basis for implementing support for any language, not just Scala.
+The language server may be backed up by [ensime](http://ensime.github.io/) or directly by the presentation compiler. Ideally, the language server ca be used as a basis for implementing support for any language, not just Scala.
+
+# How to try it out
+
+tl;dr
+
+```bash
+$ sbt publishExtension
+$ cd scala
+$ vsce package
+```
+
+You shuld see a file `ensime-scala-0.0.3.vsix` (or whatever version you are building). Now install it in Code by choosing `Install from VSIX` in the Extensions view.
+
+## Building
+
+The root Sbt project controls all the Scala parts of the build. The client is written in Typescript (it's really minimal) and lives under scala/. This one is built using Code's tools.
+
+- languageserver/ contains the language-independent server implementation. It does not implement the full protocol yet. Features are added by-need, when the reference implementation in ensime-server/ needs it
+- ensime-server/ implements an Ensime based Scala language server
+- scala/ The typescript extension (eventually should migrate to Scala.js)
+
+The ensime-server is what you will want to build most of the times. It's using `assembly` to build a fat jar, so the client can launch it as simply as possible.
+
+You should use `sbt publishExtension` which copies the fat jar into a directory under scala/server, so the client finds it easily.
+
+## Running
+
+You can open code inside the `scala/` directory and use `F5` to debug the extension. This picks up the changes in the server (make sure you copied the fat jar using `sbt publishExtension`!) and allows quick iteration.