[readme] add tested browsers

README.md

@@ -26,6 +26,19 @@ functionName.shim();
 assert.equal(function foo() {}.name, 'foo');
 ```
 
+## Supported engines
+Automatically tested in every minor version of node.
+
+Manually tested in:
+ - Safari: v4 - v15 <sub>(4, 5, 5.1, 6.0.5, 6.2, 7.1, 8, 9.1.3, 10.1.2, 11.1.2, 12.1, 13.1.2, 14.1.2, 15.3, 15.6.1)</sub>
+ - Chrome: v15 - v81, v83 - v106<sub>(every integer version)</sub>
+   - Note: This includes Edge v80+ and Opera v15+, which matches Chrome
+ - Firefox: v3, v3.6, v4 - v105 <sub>(every integer version)</sub>
+   - Note: in v42 - v63, `Function.prototype.toString` throws on HTML element constructors, or a Proxy to a function
+   - Note: in v20 - v35, HTML element constructors are not callable, despite having typeof `function`
+ - IE: v6 - v11<sub>(every integer version</sub>
+ - Opera: v11.1, v11.5, v11.6, v12.0, v12.1, v12.14, v12.15, v12.16, v15+ <sub>v15+ matches Chrome</sub>
+
 ## Tests
 Simply clone the repo, `npm install`, and run `npm test`