docs: correct manual link

Author: Tieqiong

news/doctab.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* Changed the removed local manual link to the online page.
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

src/diffpy/pdfgui/gui/mainframe.py

@@ -2522,10 +2522,8 @@ def onSaveCalc(self, event):
     def onDocumentation(self, event):
         """Show information about the documentation."""
         import webbrowser
-        from urllib.request import pathname2url
-
-        url = "file://" + pathname2url(docMainFile)
-        webbrowser.open(url)
+        
+        webbrowser.open(docMainFile)
         return
 
     # MISC INTERACTION ITEMS

src/diffpy/pdfgui/gui/pdfguiglobals.py

@@ -55,7 +55,7 @@
 APPDATADIR = os.path.abspath(APPDATADIR)
 
 # Location of the HTML manual
-docMainFile = os.path.join(APPDATADIR, "doc/manual/pdfgui.html")
+docMainFile = "https://diffpy.github.io/diffpy.pdfgui/manual.html"
 
 del _upbasedir
 del _development_mode