UI String Updates for Raw HTML Editor Change

Modified the Raw HTML template text and the help string for the Editor
setting.

common/lib/xmodule/xmodule/html_module.py

@@ -37,7 +37,7 @@ class HtmlFields(object):
         scope=Scope.settings
     )
     editor = String(
-        help="Supports switching between the Visual Editor and the Raw HTML Editor. The change does not take effect until Save is pressed.",
+        help="Select Visual to enter content and have the editor automatically create the HTML. Select Raw to edit HTML directly. If you change this setting, you must save the component, then re-open it for editing.",
         display_name="Editor",
         default="visual",
         values=[

common/lib/xmodule/xmodule/templates/html/raw.yaml

@@ -3,4 +3,13 @@ metadata:
     display_name: Raw HTML
     editor: raw
 data: |
-      <p>For use with complex HTML, to allow complete control over the final product.</p>
+      <p>This template is similar to the Text template. The only difference is 
+      that this template opens in a raw HTML editor rather than in the Visual 
+      editor. Raw HTML is most useful when you need to use script and span tags 
+      to format your content.</p>
+
+      <p>The raw HTML editor saves your HTML exactly as you enter it. 
+      You can switch to the Visual editor by clicking the Settings tab and 
+      changing the Editor setting to Visual. Note, however, that some of your 
+      HTML may be modified when you save the component if you switch to the 
+      Visual editor.</p>