Update documentation for backup slides

doc/metropolistheme.dtx

@@ -497,6 +497,18 @@ The sub-package |pgfplotsthemetol| defines palettes for |pgfplots| charts
 based on Tol's work.
 
 
+\section{Tips \& Tricks}
+
+\subsection{Backup Slides}
+
+Speakers will often include extra slides at the end of their presentation to
+refer to during audience questions. One easy way to do this is to include the
+\verb|appendixnumberbeamer| package in your preamble and call \verb|\appendix| before your backup slides.
+
+\themename will automatically turn off slide numbering and progress bars for
+slides in the appendix.
+
+
 \section{Known Issues}
 
 \subsection{Title formats}

source/beamerouterthememetropolis.dtx

@@ -187,6 +187,10 @@
 %
 %
 % \begin{macro}{appendix}
+%    Removes page numbering and per-slide progress bars when |\appendix| is
+%    called. This makes it easier to include additional ``backup slides'' at
+%    the end of the presentation, especially in conjunction with the package
+%    |appendixnumberbeamer|.
 %    \begin{macrocode}
 \AtBeginDocument{%
   \apptocmd{\appendix}{%