Add some sensible content to vscode-boot-java readme

vscode-extensions/vscode-boot-java/DEVELOPER-NOTES.md

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+# Developer notes
+
+## Bulding and Running
+
+This project consists of three pieces:
+
+ - a vscode-extension which is a language-server client implemented in TypeScript.
+ - commons-vscode: a local npm module with some utilities implemented in TypeScript.
+ - a language server implemented in Java.
+
+To build all these pieces you normally only need to run:
+
+   npm install
+
+**However, the first time you build** it might fail trying to
+find the `commons-vscode` module on npm central. Once we publish a stable 
+version of that module on npm central that will no longer be a problem. 
+Until that time, you can work around this by doing a one time manual 
+run of the `preinstall` script prior to running `npm install`:
+
+    ./scripts/preinstall.sh
+    npm install
+
+Now you can open the client-app in vscode. From the root of this project.
+
+    code .
+
+To launch the language server in a vscode runtime, press F5.
+
+## Debugging
+
+### Method 1: attach remote debugger to Language Server
+
+To debug the language server, open `lib/Main.ts` and edit to set the
+`DEBUG` option to `true`. When you launch the app next by pressing
+`F5` it will launch with debug options being passed to the server JVM.
+
+You can then connect a 'Remote Java' debugger on port 8000.
+
+### Method 2: Launch a 'standalone' Language Server
+
+To debug the language server, open `lib/Main.ts` and edit to set the
+`CONNECT_TO_LS` option to `true`. When you launch the app next by pressing
+`F5`... When it needs a language server it not launch a process but instead
+try to connect to an already running server on port `5007`. It is up to you
+to ensure a server is running on that port by launching it beforehand 
+with a commandline arguments: `-Dstandalone-startup=true`.
+
+## Packaging as a vscode extension
+
+First make sure the stuff is all built locally:
+
+     ./scripts/preinstall.sh  # only needed if this is the first build.
+     npm install
+
+Then package it:
+
+     npm run vsce-package
+
+This produces a `.vsix` file which you can install directly into vscode.