chore(record-picker): add some comments

force-app/main/default/lwc/recordPickerDynamicTarget/recordPickerDynamicTarget.html

@@ -8,6 +8,7 @@
             <label class="slds-form-element__label">Select a record</label>
             <div class="slds-form-element__control slds-combobox-group">
                 <template if:true={showTargetSelector}>
+                    <!-- Target selector -->
                     <lightning-combobox
                         data-id="targetSelector"
                         label="Select a target sObject"

force-app/main/default/lwc/recordPickerDynamicTarget/recordPickerDynamicTarget.js

@@ -1,5 +1,9 @@
 import { LightningElement } from 'lwc';
 
+// As of today, `lightning-record-picker` only supports a single target.
+// This sample component shows how you can turn `lightning-record-picker` into
+// a multi-target record picker, where the user can select the target object
+// before searching.
 export default class RecordPickerDynamicTarget extends LightningElement {
     targetObjects = [
         {
@@ -45,6 +49,9 @@ export default class RecordPickerDynamicTarget extends LightningElement {
     }
 
     handleTargetSelection(event) {
+        // Prevent lightning-combobox `change` event from bubbling
+        event.stopPropagation();
+
         this.selectedTarget = event.target.value;
         this.refs.recordPicker.clearSelection();
     }

force-app/main/default/lwc/recordPickerHello/recordPickerHello.js

@@ -16,6 +16,9 @@ export default class RecordPickerHello extends LightningElement {
         this.selectedRecordId = event.detail.recordId;
     }
 
+    // A GraphQL query is sent after the record picker change event has been dispatched.
+    // This is the recommended practice for fetching record fields based on
+    // the record picker change event's recordId.
     @wire(graphql, {
         query: gql`
             query searchContacts($selectedRecordId: ID) {