nixos-render-docs: indent and embolden list item heads in manpages

this matches what html outputs do more closely, and feels like it'll be
easier to read because it looks less like just another paragraph.

pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/manpage.py

@@ -177,7 +177,7 @@ class ManpageRenderer(Renderer):
         return (
             f'{maybe_space}'
             f'.RS {lst.width}\n'
-            f"\\h'-{lst.width}'{man_escape(head)}\\h'{lst.width - len(head)}'\\c"
+            f"\\h'-{len(head) + 1}'\\fB{man_escape(head)}\\fP\\h'1'\\c"
         )
     def list_item_close(self, token: Token, tokens: Sequence[Token], i: int, options: OptionsDict,
                         env: MutableMapping[str, Any]) -> str: