Add missing commands with overlay specification [ci skip]

- `\emph`
- `\textcolor`

doc/beamerug-overlays.tex

@@ -121,7 +121,7 @@ \subsection{Commands with Overlay Specifications}
 commands documented here are \emph{all} fragile even if the \LaTeXe{} kernel
 versions are not.
 
-For the following commands, adding an overlay specification causes the command to be simply ignored on slides that are not included in the specification: |\textbf|, |\textit|, |\textsl|, |\textrm|, |\textsf|, |\color|, |\alert|, |\structure|. If a command takes several arguments, like |\color|, the specification should directly follow the command as in the following example (but there are exceptions to this rule):
+For the following commands, adding an overlay specification causes the command to be simply ignored on slides that are not included in the specification: |\textbf|, |\textit|, |\textrm|, |\textsl|, |\textsf|, |\emph|; |\color|, |\textcolor|; |\alert|, |\structure|. If a command takes several arguments, like |\color|, the specification should directly follow the command as in the following example (but there are exceptions to this rule):
 \begin{verbatim}
 \begin{frame}
   \color<2-3>[rgb]{1,0,0} This text is red on slides 2 and 3, otherwise black.