docs(change-log): update for move to @typings (#2643)

Author: wardbell

public/docs/ts/latest/guide/change-log.jade

@@ -7,6 +7,15 @@ block includes
   The Angular documentation is a living document with continuous improvements.
   This log calls attention to recent significant changes.
 
+  ## npm _@types_ packages replace _typings_ (2016-10-20)
+  Documentation samples now get TypeScript type information for 3rd party libraries
+  from npm `@types` packages rather than with the _typings_ tooling.
+  The `typings.json` file is gone.
+
+  The "[Angular 1 Upgrade](upgrade.html)" guide reflects this change.
+  The `package.json` installs `@types/angular` and several `@types/angular-...`
+  packages in support of upgrade; these are not needed for pure Angular 2 development.
+
   ## "Template Syntax" explains two-way data binding syntax (2016-10-20)
   Demonstrates how to two-way data bind to a custom Angular component and
   re-explains `[(ngModel)]` in terms of the basic `[()]` syntax.