Readme: add dev build instructions (#3)

Readme.md

@@ -1,5 +1,32 @@
 # hyperterm
 
+## Developing
+
+To install `package.json` dependencies in a way where the native
+modules are built with `electron`, run:
+
+```bash
+$ ./install.sh
+```
+
+Then, you want to make sure `app/dist` is populated. I recommend
+running `webpack` with `--watch` so that any changes you make
+to the app are detected.
+
+```bash
+$ cd app/
+$ npm install
+$ webpack --watch
+```
+
+Then you can run:
+
+```bash
+$ electron index
+```
+
+to launch the app!
+
 ## TODO
 
 - [ ] Warn upon quit