docs(operators): add documentation for operator do

src/operator-docs/utility/do.ts

@@ -1,6 +1,73 @@
 import { OperatorDoc } from '../operator.model';
 
 export const doOperator: OperatorDoc = {
-  'name': 'do',
-  'operatorType': 'utility'
+  name: 'do',
+  operatorType: 'utility',
+  signature:
+    'public do(nextOrObserver: Observer | function, error: function, complete: function): Observable',
+  parameters: [
+    {
+      name: 'nextOrObserver',
+      type: 'Observer|function',
+      attribute: 'optional',
+      description: 'A normal Observer object or a callback for `next`.'
+    },
+    {
+      name: 'error',
+      type: 'function',
+      attribute: 'optional',
+      description: 'Callback for errors in the source.'
+    },
+    {
+      name: 'complete',
+      type: 'function',
+      attribute: 'optional',
+      description: 'Callback for the completion of the source.'
+    }
+  ],
+  marbleUrl: 'http://reactivex.io/rxjs/img/do.png',
+  shortDescription: {
+    description: `Perform a side effect for every emission on the source Observable, but return
+      an Observable that is identical to the source.
+      <span class="informal">Intercepts each emission on the source and runs a
+      function, but returns an output which is identical to the source as long as errors don't
+      occur.</span>`
+  },
+  walkthrough: {
+    description: `
+      <p>Returns a mirrored Observable of the source Observable,
+      but modified so that the provided Observer is called to perform a side effect for every
+      value, error, and completion emitted by the source. Any errors that are thrown in
+      the aforementioned Observer or handlers are safely sent down the error path
+      of the output Observable.
+      </p>
+      <p>
+      This operator is useful for debugging your Observables for the correct values
+      or performing other side effects.
+      </p>
+      <p>
+      Note: this is different to a <code>subscribe</code> on the Observable. If the Observable
+      returned by <code>do</code> is not subscribed, the side effects specified by the
+      Observer will never happen. <code>do</code> therefore simply spies on existing
+      execution, it does not trigger an execution to happen like <code>subscribe</code> does.</p>
+    `
+  },
+  examples: [
+    {
+      name:
+        'Map every click to the clientX position of that click, while also logging the click event',
+      code: `
+      var clicks = Rx.Observable.fromEvent(document, 'click');
+      var positions = clicks
+         .do(ev => console.log(ev.type))
+         .map(ev => ev.clientX);
+      positions.subscribe(x => console.log(x));
+      `,
+      externalLink: {
+        platform: 'JSBin',
+        url: 'http://jsbin.com/mikiqub/edit?js,console,output'
+      }
+    }
+  ],
+  relatedOperators: ['map', 'subscribe']
 };