Add browserstack logo to get access to their open source plan

Author: carols10cents

README.md

@@ -28,6 +28,12 @@ variety of skill levels.
 Please see [docs/CONTRIBUTING.md](https://github.com/rust-lang/crates.io/blob/master/docs/CONTRIBUTING.md) for ideas about what to work on and how to set up a development
 environment.
 
+<a href="https://www.browserstack.com">
+    <img src="browserstack-logo.png" alt="BrowserStack" />
+</a>
+
+We also use [BrowserStack](https://www.browserstack.com) to help us verify that the frontend works in all of our supported browsers. Thanks, BrowserStack!
+
 ### Categories
 
 Adding or editing the categories and corresponding descriptions displayed on