talk about --resource-suffix

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

@@ -316,3 +316,16 @@ $ rustdoc -Z unstable-options --theme-checker theme.css
 Before including your theme in crate docs, `rustdoc` will compare all the CSS rules it contains
 against the "main" theme included by default. Using this flag will allow you to see which rules are
 missing if `rustdoc` rejects your theme.
+
+### `--resource-suffix`: modifying the name of CSS/JavaScript in crate docs
+
+Using this flag looks like this:
+
+```bash
+$ rustdoc src/lib.rs -Z unstable-options --resource-suffix suf
+```
+
+When rendering docs, `rustdoc` creates several CSS and JavaScript files as part of the output. Since
+all these files are linked from every page, changing where they are can be cumbersome if you need to
+specially cache them. This flag will rename all these files in the output to include the suffix in
+the filename. For example, `main.css` would become `main-suf.css` with the above command.