Add edit-tab help.

lib/python/Products/PageTemplates/help/PageTemplate_Edit.stx

+Edit View: Edit A Page Template
+  
+    Description
+
+        This view allows you to edit the template's text, upload new
+        text, or change the content type and title of the template.
+
+    Template Text
+
+        The text in a template must be well-formed HTML if the content
+        type is 'text/html'.  Otherwise, it must be well-formed XML.
+        Either way, it may include "TAL":tal.stx or "METAL":metal.stx
+        markup containing "TALES":tales.stx expressions.
+        
+    Controls
+
+        'Title' -- Allows you to specify the Zope title of the template.
+        
+        'Content-Type' -- Allows you to specify the content-type that
+        will be given to renderings of this template.
+        
+    Buttons and Other Form Elements
+
+        'Save Changes' -- saves changes you make to the body, title, or
+          content type.
+
+        'Taller'/'Shorter'/'Wider'/'Narrower' -- make the body textarea
+          taller, shorter, wider, or narrower.
+
+        'File' -- upload a file into this template.
+
+    File Upload Details
+
+        Files uploaded into a template must be valid HTML or XML text.
+