AngularJS Change Sets - Update title. Add intro para.

docs/framework/angular/modify.md

-# AngularJS: Alteration
+# AngularJS: Change Sets
+
+The [Quick Start](quickstart.md) and [Loader](loader.md) provide examples of
+creating *new* screens.  But what if you need to alter an *existing* screen?
+CiviCRM allows third-parties to define *change sets* which programmatically
+manipulate Angular content (before sending it to the client).
+
+## Background
+
+Most AngularJS tutorials focus on idealized projects where a single
+developer or product-owner exercises full authority over their application.
+But CiviCRM is an _ecosystem_ with a range of stakeholders, including many
+developers (authoring indpendent extensions) and administrators (managing
+independent deployments with independent configurations).
+
+...
+
+## tldr
 
 ```php
-function example_civicrm_alterAngular($angular) {
-  $angular->add(\Civi\Angular\ChangeSet::create('mychanges')
-    ->alterHtml('~/crmMailing/EditMailingCtrl/2step.html', function(phpQueryObject $doc) {
-      $doc->find('[ng-form="crmMailingSubform"]')->attr('cat-stevens', 'ts(\'wild world\')');
-    })
-  );
+function mailwords_civicrm_alterAngular(\Civi\Angular\Manager $angular) {
+  $changeSet = \Civi\Angular\ChangeSet::create('inject_mailwords')
+    // ->requires('crmMailing', 'mailwords')
+    ->alterHtml('~/crmMailing/BlockSummary.html',
+      function (phpQueryObject $doc) {
+        $doc->find('.crm-group')->append('
+        <div crm-ui-field="{name: \'subform.mailwords\', title: ts(\'Keywords\')}">
+          <input crm-ui-id="subform.mailwords" class="crm-form-text" name="mailwords" ng-model="mailing.template_options.keywords">
+        </div>
+      ');
+      });
+  $angular->add($changeSet);
 }
 ```
 
-
 cv ang:html:show
\ No newline at end of file

mkdocs.yml

@@ -48,7 +48,7 @@ pages:
     - Quick Start: framework/angular/quickstart.md
     - File Names: framework/angular/files.md
     - Loader: framework/angular/loader.md
-    - Modifications:  framework/angular/modify.md
+    - Change Sets:  framework/angular/modify.md
   - Asset Builder: framework/asset-builder.md
   # Bootstrap: /framework/bootstrap.md
   # Cache: /framework/cache.md