Use Mutt cache to improve loading speed

beaglebone.txt

@@ -1175,6 +1175,7 @@ set postponed="+.Drafts"
 set spoolfile="~/Maildir"
 auto_view text/x-vcard text/html text/enriched
 set editor="emacsclient %s"
+set header_cache="+.cache"
 
 macro index S "<tag-prefix><save-message>=.learn-spam<enter>" "move to learn-spam"
 macro pager S "<save-message>=.learn-spam<enter>" "move to learn-spam"