[jquery] Add README describing usage and guidance for authoring jQuery plugin typedefs.

types/jquery/README.md

@@ -0,0 +1,53 @@
+### Usage
+
+#### Global
+
+When jQuery is globally available, you can use `jQuery` and `$` directly.
+
+#### Importing (with a global DOM available)
+
+When you want to import jQuery as a module and have a global DOM available (e.g. browser and browser-like environments):
+
+```typescript
+import * as jQuery from 'jquery';
+```
+
+#### Importing (without a global DOM available)
+
+When you want to import jQuery as a module and do not have a global DOM available (e.g. Node.js environment):
+
+```typescript
+import jQueryFactory = require('jquery');
+const jQuery = jQueryFactory(window, true);
+```
+
+Note that while the factory function ignores the second parameter, it is required to get correct type declarations.
+
+### Authoring type definitions for jQuery plugins
+
+`$.fn` is represented by `JQuery`.
+
+`$` is represented by `JQueryStatic`.
+
+Declare an interface that has the plugin's overloads as call signatures and static members as properties.
+
+```typescript
+interface MyPlugin {
+    settings: MyPluginSettings;
+    
+    (behavior: 'enable'): JQuery;
+    (settings?: MyPluginSettings): JQuery;
+}
+
+interface MyPluginSettings {
+    title?: string;
+}
+```
+
+Then declare a property on `JQuery` with your plugin's type.
+
+```typescript
+interface JQuery {
+    myPlugin: MyPlugin;
+}
+```