add descriptive comment to top of HTML file

libs/auth/src/angular/login/login.component.html

@@ -1,7 +1,32 @@
+<!-- 
+  # Table of Contents
+
+    This file contains three templates, one for each visual client.
+    
+    For easy navigation, search for the following phrases:
+      Web Template
+      Browser Template
+      Desktop Template
+
+    Or simply collapse the templates you are not working on in your editor.
+
+  # UI States
+
+    Each client template is split into two UI states:
+      State 1: displays the email input field + continue button
+      State 2: displays the master password input field + login button
+    
+    These are defined by the `LoginUiState` enum:
+
+      enum LoginUiState {
+        EMAIL_ENTRY = "EmailEntry",
+        MASTER_PASSWORD_ENTRY = "MasterPasswordEntry",
+      }
+-->
+
 <!--------------------------------->
 <!--        Web Template         -->
 <!--------------------------------->
-
 <!--
     TODO-rr-bw: Clarify this comment if necessary.