Mention necessary . -> - replacement for intro vignette (r-lib#2307)

man/rmd-fragments/navbar-configuration.Rmd

@@ -13,14 +13,17 @@ navbar:
 
 It makes use of the the six built-in components:
 
--   `intro`: "Get Started", which links to a vignette with the same name as the package.
+-   `intro`: "Get Started", which links to a vignette with the same name as the package[^dots].
 -   `reference`, if there are any `.Rd` files.
 -   `articles`, if there are any vignettes or articles.
 -   `tutorials`, if there any tutorials.
 -   `news`, if `NEWS.md` exists.
 -   `search`, the search box (see `vignette("search")` for more details).
 -   `github`, a link to the source repository (with an icon), if it can be automatically determined from the `DESCRIPTION`.
 
+[^dots]: Note that dots (`.`) in the package name need to be replaced by hyphens (`-`) in the vignette filename to be recognized as the intro. That means for a
+    package `foo.bar` the intro needs to be named `foo-bar.Rmd`.
+
 You can use the `structure` field to reorganise the navbar without changing the default contents:
 
 ``` yaml