docs: state default plugin set and reframe stock themes as rarely used alternatives

Change-Id: Id5a37a34b4351fe17fa5c4d32572db6da2d44f04
diff --git a/man/revealjs_presentation.Rd b/man/revealjs_presentation.Rd
index 0e93d1a..84033ba 100644
--- a/man/revealjs_presentation.Rd
+++ b/man/revealjs_presentation.Rd
@@ -69,7 +69,11 @@
 or just the body of a LaTeX document (\code{FALSE}). Note the LaTeX
 document is an intermediate file unless \code{keep_tex = TRUE}.}
 
-\item{theme}{Visual theme ("ids", "simple", "dark", "black", "sky", "beige", "serif", "solarized", "blood", "moon", "night", "league", or "white")}
+\item{theme}{Visual theme. Defaults to the dedicated IDS corporate design
+theme ("ids"), which is the raison d'être of this package; the stock
+reveal.js themes are available as rarely used alternatives:
+"simple", "dark", "black", "sky", "beige", "serif", "solarized", "blood", "moon", "night", "league", or "white"
+("dark" is an alias for "black").}
 
 \item{transition}{Slide transition (
 "convex", "fade", "slide", "concave", "zoom", or "none"
@@ -155,15 +159,18 @@
 \url{https://github.com/rstudio/revealjs}
 }
 \section{About plugins}{
+The plugins \code{notes}, \code{search}, \code{menu} and \code{zoom} are activated by default;
+only \code{chalkboard} is opt-in. Setting \code{reveal_plugins} replaces the default
+set -- pass \code{NULL} to render without any plugins.
 \subsection{Built-in plugins with reveal.js}{
 \subsection{Zoom}{
 
-When activated, ALT + Click can be used to zoom on a slide.
+Activated by default: ALT + Click can be used to zoom on a slide.
 }
 
 \subsection{Notes}{
 
-Show a \href{https://revealjs.com/speaker-view/}{speaker view} in a separated
+Activated by default: shows a \href{https://revealjs.com/speaker-view/}{speaker view} in a separated
 window. This speaker view contains a timer, current slide, next slide, and
 speaker notes. It also duplicate the window to have presentation mode
 synchronized with main presentation.
@@ -249,7 +256,8 @@
 their sub-slides.
 \subsection{Search}{
 
-When opt-in, it is possible to show a search box when pressing \code{CTRL + SHIFT + F}. It will seach in the whole presentation, and highlight matched words. The
+Activated by default: pressing \code{CTRL + SHIFT + F} shows a search box.
+It will search in the whole presentation, and highlight matched words. The
 matches will also be highlighted in overview mode (pressing ESC to see all
 slides in one scrollable view)
 }
@@ -258,7 +266,8 @@
 
 \subsection{Menu}{
 
-A slideout menu plugin for Reveal.js to quickly jump to any slide by title.
+Activated by default: a slideout menu plugin for Reveal.js to quickly jump
+to any slide by title.
 
 Version  is
 currently used and documentation for configurations can be found at
@@ -279,7 +288,7 @@
 
 \subsection{Chalkboard}{
 
-A plugin adding a chalkboard and slide annotation
+An opt-in plugin adding a chalkboard and slide annotation
 
 Version  is
 currently used and documentation for configurations can be found at