Add stores section with Chrome and Firefox listing links to browser extension README

- add links to stores in `apps/browser/README.md`

├── README.md
└── apps
    ├── browser
    │   └── README.md
    └── editor
        └── src
            └── views
                └── prompt
                    └── backend
                        └── message-handlers
                            └── handle-install-browser-extension.ts

Author: robertpiosik

apps/browser/README.md

@@ -13,6 +13,11 @@ Serves two purposes:
 > [!IMPORTANT]
 > Prompt text is never submitted or response accepted automatically.
 
+## Stores
+
+- [Chrome Web Store](https://chromewebstore.google.com/detail/autofill-for-code-web-chat/ljookipcanaglfaocjbgdicfbdhhjffp)
+- [Firefox Add-ons](https://addons.mozilla.org/en-US/firefox/addon/autofill-for-code-web-chat/)
+
 ## Permissions
 
 The extension functions with minimal permissions.