head: add meta robots

- disable indexing for non-prod sites

layouts/partials/head.html

@@ -1,6 +1,11 @@
 <meta charset="utf-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+{{- if eq (getenv "HUGO_ENV") "production" | or (eq .Site.Params.env "production") }}
+<meta name="robots" content="index, follow">
+{{- else }}
+<meta name=" robots" content="noindex, nofollow">
+{{- end -}}
 <!-- Title -->
 <title>{{ if .IsHome }}{{else}}{{ if .Title }}{{ .Title }} - {{ end }}{{end}}{{ .Site.Title }}</title>
 <!-- Meta -->