docs(overmind-devtools): document local setup

Author: dpraimeyuu

packages/overmind-devtools/README.md

@@ -1,3 +1,22 @@
-# overmind-devtools
+### Introduction
 
-To be filled
+This package is one of three packages related to `overmind-devtools`.
+
+If you're looking for a little deeper insight about these, please check [overmind-devtools-client](../overmind-devtools-client/README.md).
+
+### Local development
+
+**PREREQUISITE**: make sure you firstly [built](../overmind-devtools-client/README.md) devtools UI core so that it can be hosted by this package (electron application).
+
+Considering the above prerequisite is satisfied, run the following steps:
+1. Build the host:
+```sh
+npm run build
+```
+2. Run the application:
+```sh
+npm run prod
+```
+3. Use `Application` tab and then clicking on `Open Chrome DevTools`:
+
+![overmind-devtools-debugging](./docs/assets/overmind-devtools-debugging.png)