docs: the nvim plugins have to be installed, not worked around

silent! on the colorscheme stops nvim erroring on a machine where PlugInstall
has never run, but it does not give you gruvbox - it gives you the default
theme without saying so. That is a safety net for the gap between checkout and
install, not a fix.

Setting up a machine now lists both steps: packages.sh for the system packages
and PlugInstall for the ten nvim plugins. Also noted that firenvim reports "No
config detected" for every browser on a headless host, which looks like a
failure and is not.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -133,6 +133,21 @@ config config --local status.showUntrackedFiles no
 config checkout master
 ```
 
+Then install what the configuration files expect but do not carry:
+
+```sh
+.scripts/packages.sh install                    # system packages for the role
+nvim --headless "+PlugInstall --sync" +qall     # the nvim plugins
+```
+
+The nvim step matters more than it looks. gruvbox is a plugin, and until
+`PlugInstall` has run, nvim comes up in the default theme. The `colorscheme`
+line is wrapped in `silent!` so a fresh machine does not error before then —
+that is a safety net for the gap, not a substitute for installing them.
+
+On a headless machine `firenvim` will report "No config detected" for every
+browser it looks for. That is expected and harmless.
+
 > Earlier revisions of this file used `curl -Lks`. The `-k` disables
 > certificate verification against a host that has a valid certificate,
 > removing precisely the protection that matters when piping a remote script