Move browser extension into DrupalPod repository

[mradcliffe]

Is your feature request related to a problem? Please describe

Follow-up from #27

Describe the solution you'd like

1. Moves shaal/drupalpod-browser-extension
2. Adds contribution instructions

Directory structure from shaal:

src
├── browser-extension
│   └── drupalpod-browser-extension
│       ├── css
│       │   ├── options.css
│       │   └── popup.css
│       ├── icons
│       │   ├── DrupalPod-128.png
│       │   └── DrupalPod-128x128.png
│       ├── LICENSE
│       ├── manifest.json
│       ├── options.html
│       ├── popup.html
│       ├── README.md
│       └── scripts
│           ├── background.js
│           ├── options.js
│           └── popup.js
├── composer
│   └── ComposerScripts.php
└── vscode-extension
    └── drupalpod-ext
        ├── CHANGELOG.md
        ├── package.json
        ├── README.md
        ├── src
        │   ├── extension.ts
        │   ├── help-content.ts
        │   └── test
        │       ├── runTest.ts
        │       └── suite
        │           ├── extension.test.ts
        │           └── index.ts
        ├── tsconfig.json
        └── yarn.lock

Describe alternatives you've considered

Additional context