Update documentation about themes

Author: GuillaumeGomez

src/doc/rustdoc/src/how-to-read-rustdoc.md

@@ -59,15 +59,8 @@ or the current item whose documentation is being displayed.
 ## The Theme Picker and Search Interface
 
 When viewing `rustdoc`'s output in a browser with JavaScript enabled,
-a dynamic interface appears at the top of the page.
-To the left is the theme picker, denoted with a paint-brush icon,
-and the search interface, help screen, and options appear to the right of that.
-
-### The Theme Picker
-
-Clicking on the theme picker provides a list of themes -
-by default `ayu`, `light`, and `dark` -
-which are available for viewing.
+a dynamic interface appears at the top of the page composed of the search
+interface, help screen, and options.
 
 ### The Search Interface
 
@@ -91,12 +84,16 @@ When typing in the search bar, you can prefix your search term with a type
 followed by a colon (such as `mod:`) to restrict the results to just that
 kind of item. (The available items are listed in the help popup.)
 
+### Changing displayed theme
+
+You can change the displayed theme by opening the settings menu (the gear
+icon in the upper right) and then pick a new one from there.
+
 ### Shortcuts
 
 Pressing `S` while focused elsewhere on the page will move focus to the
 search bar, and pressing `?` shows the help screen,
 which includes all these shortcuts and more.
-Pressing `T` focuses the theme picker.
 
 When the search results are focused,
 the left and right arrows move between tabs and the up and down arrows move

src/doc/rustdoc/src/write-documentation/what-to-include.md

@@ -109,8 +109,9 @@ rustdoc --extend-css custom.css src/lib.rs
 
 A good example of using this feature to create a dark theme is documented [on
 this blog].  Just remember, dark theme is already included in the rustdoc output
-by clicking on the paintbrush.  Adding additional options to the themes are
-as easy as creating a custom theme `.css` file and using the following syntax:
+by clicking on the gear icon in the upper right. Adding additional options to the
+themes are as easy as creating a custom theme `.css` file and using the following
+syntax:
 
 ```bash
 rustdoc --theme awesome.css src/lib.rs