Add Website features page to rustdoc book

Author: jeanlucthumm

src/doc/rustdoc/src/SUMMARY.md

@@ -10,5 +10,6 @@
 - [Lints](lints.md)
 - [Advanced features](advanced-features.md)
 - [Unstable features](unstable-features.md)
+- [Website features](website-features.md)
 - [Passes](passes.md)
 - [References](references.md)

src/doc/rustdoc/src/website-features.md

@@ -0,0 +1,21 @@
+# Website features
+
+These features are about using the website generated by `rustdoc`.
+
+## Custom search engines
+
+If you find yourself often referencing online Rust docs you might enjoy using a custom search
+engine. This allows you to use the navigation bar directly to search a `rustdoc` website.
+Most browsers support this feature by letting you define a URL template containing `%s`
+which will be substituted for the search term. As an example, for the standard library you could use
+this template:
+```
+https://doc.rust-lang.org/stable/std/?search=%s
+```
+Note that this will take you to a results page listing all matches. If you want to navigate to the first
+result right away (which is often the best match) use the following instead:
+```
+https://doc.rust-lang.org/stable/std/?search=%s&go_to_first=true
+```
+This URL adds the `go_to_first=true` query parameter which can be appended to any `rustdoc` search URL
+to automatically go to the first result.