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

Change-Id: Id5a37a34b4351fe17fa5c4d32572db6da2d44f04
diff --git a/R/revealjs_presentation.R b/R/revealjs_presentation.R
index d28fcd8..fa31dca 100644
--- a/R/revealjs_presentation.R
+++ b/R/revealjs_presentation.R
@@ -11,16 +11,20 @@
 #' <https://github.com/rstudio/revealjs>
 #' 
 #' # About plugins
-#' 
+#'
+#' The plugins `notes`, `search`, `menu` and `zoom` are activated by default;
+#' only `chalkboard` is opt-in. Setting `reveal_plugins` replaces the default
+#' set -- pass `NULL` to render without any plugins.
+#'
 #' ## Built-in plugins with reveal.js
-#' 
-#' ### Zoom 
-#' 
-#' When activated, ALT + Click can be used to zoom on a slide.
-#' 
-#' ### Notes 
-#'  
-#' Show a [speaker view](https://revealjs.com/speaker-view/) in a separated
+#'
+#' ### Zoom
+#'
+#' Activated by default: ALT + Click can be used to zoom on a slide.
+#'
+#' ### Notes
+#'
+#' Activated by default: shows a [speaker view](https://revealjs.com/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.
@@ -103,15 +107,16 @@
 #' their sub-slides.
 #' 
 #' ### Search
-#' 
-#' When opt-in, it is possible to show a search box when pressing `CTRL + SHIFT +
-#' F`. It will seach in the whole presentation, and highlight matched words. The
+#'
+#' Activated by default: pressing `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)
 #' 
-#' ## Menu 
-#' 
-#' A slideout menu plugin for Reveal.js to quickly jump to any slide by title.
+#' ## Menu
+#'
+#' Activated by default: a slideout menu plugin for Reveal.js to quickly jump
+#' to any slide by title.
 #' 
 #' Version `r version <- readLines(revealjs_lib_path("plugin", "menu", "VERSION"))` is
 #' currently used and documentation for configurations can be found at
@@ -127,9 +132,9 @@
 #' * `themes: false`
 #' * `transitions: false`
 
-#' ## Chalkboard 
-#' 
-#' A plugin adding a chalkboard and slide annotation
+#' ## Chalkboard
+#'
+#' An opt-in plugin adding a chalkboard and slide annotation
 #' 
 #' Version `r version <- readLines(revealjs_lib_path("plugin", "chalkboard", "VERSION"))` is
 #' currently used and documentation for configurations can be found at
@@ -164,7 +169,11 @@
 #'   produced, with level 1 headers building horizontally and level 2 headers
 #'   building vertically. It is not recommended that you use deeper nesting of
 #'   section levels with reveal.js.
-#' @param theme Visual theme (`r knitr::combine_words(setdiff(revealjs_themes(), "default"), before = '"', and = " or ")`)
+#' @param 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:
+#'   `r knitr::combine_words(setdiff(revealjs_themes(), c("default", "ids")), before = '"', and = " or ")`
+#'   ("dark" is an alias for "black").
 #' @param transition Slide transition (
 #' `r (trans <- knitr::combine_words(setdiff(revealjs_transitions(), "default"), before = '"', and = " or "))`
 #' )