docs(aio): add Observable and Rx docs (#21423)

PR Close #21423

aio/content/examples/rx-library/src/operators.1.ts

@@ -0,0 +1,25 @@
+import { Observable } from 'rxjs/Observable';
+import 'rxjs/add/observable/of';
+
+// #docregion
+
+import { pipe } from 'rxjs/util/pipe';
+import { filter, map } from 'rxjs/operators';
+
+const nums = Observable.of(1, 2, 3, 4, 5);
+
+// Create a function that accepts an Observable.
+const squareOddVals = pipe(
+  filter(n => n % 2),
+  map(n => n * n)
+);
+
+// Create an Observable that will run the filter and map functions
+const squareOdd = squareOddVals(nums);
+
+// Suscribe to run the combined functions
+squareOdd.subscribe(x => console.log(x));
+
+// #enddocregion
+
+