Add documentation for sort

This adds documentation for the config option and the command.

config/aerc.conf.in

@@ -48,6 +48,15 @@ new-message-bell=true
 # Default: %n %>r
 dirlist-format=%n %>r
 
+# List of space-separated criteria to sort the messages by, see *sort*
+# command in *aerc*(1) for reference. Prefixing a criterion with "-r "
+# reverses that criterion.
+#
+# Example: "from -r date"
+#
+# Default: ""
+sort=
+
 [viewer]
 #
 # Specifies the pager to use when displaying emails. Note that some filters

doc/aerc-config.5.scd

@@ -125,6 +125,15 @@ These options are configured in the *[ui]* section of aerc.conf.
 
 	Default: ","
 
+*sort*
+	List of space-separated criteria to sort the messages by, see *sort*
+	command in *aerc*(1) for reference. Prefixing a criterion with "-r "
+	reverses that criterion.
+
+	Example: "from -r date"
+
+	Default: ""
+
 *dirlist-format*
 	Describes the format string to use for the directory list
 

doc/aerc.1.scd

@@ -192,6 +192,31 @@ message list, the message in the message viewer, etc).
 	Selects the nth message in the message list (and scrolls it into view if
 	necessary).
 
+*sort* [[-r] <criterion>]...
+	Sorts the message list by the given criteria. *-r* sorts the
+	immediately following criterion in reverse order.
+
+	Available criteria:
+
+[[ *Criterion*
+:- *Description*
+|  arrival
+:- Date and time of the messages arrival
+|  cc
+:- Addresses in the "cc" field
+|  date
+:- Date and time of the message
+|  from
+:- Addresses in the "from" field
+|  read
+:- Presence of the read flag
+|  size
+:- Size of the message
+|  subject
+:- Subject of the message
+|  to
+:- Addresses in the "to" field
+
 *view*
 	Opens the message viewer to display the selected message.