snapshot: document --export and --import options

See: https://trac.macports.org/ticket/72628
(cherry picked from commit d9a94cc142)

doc/port-snapshot.1

@@ -28,6 +28,7 @@ port-snapshot \- Manage snapshots of installed ports\&.
     [\-\-create [\-\-note <note>]]
     [\-\-list] [\-\-diff \fIsnapshot\-id\fR [\-\-all]]
     [\-\-delete \fIsnapshot\-id\fR] [\-\-help]
+    [\-\-export \fIsnapshot\-id\fR] [\-\-import \fIfilename\fR]
 .fi
 .SH "DESCRIPTION"
 .sp
@@ -64,6 +65,18 @@ Consider all ports when displaying diffs\&. By default, only differences in requ
 Delete the snapshot with the given ID number\&.
 .RE
 .PP
+\fB\-\-export ID\fR
+.RS 4
+Generate a JSON representation of the snapshot with the given ID number and print it to stdout\&.
+.RE
+.PP
+\fB\-\-import <filename>\fR
+.RS 4
+Create a new snapshot from the information in the given file, which should contain JSON as generated by the
+\fB\-\-export\fR
+option\&.
+.RE
+.PP
 \fB\-\-help\fR
 .RS 4
 Display brief usage information\&.

doc/port-snapshot.1.txt

@@ -13,6 +13,7 @@ SYNOPSIS
     [--create [--note <note>]]
     [--list] [--diff 'snapshot-id' [--all]]
     [--delete 'snapshot-id'] [--help]
+    [--export 'snapshot-id'] [--import 'filename']
 
 DESCRIPTION
 -----------
@@ -45,6 +46,14 @@ differences in requested ports are shown.
 *--delete ID*::
 Delete the snapshot with the given ID number.
 
+*--export ID*::
+Generate a JSON representation of the snapshot with the given ID number
+and print it to stdout.
+
+*--import <filename>*::
+Create a new snapshot from the information in the given file, which
+should contain JSON as generated by the *--export* option.
+
 *--help*::
 Display brief usage information.