document new history functions

doc/comitium.1.scd

@@ -67,6 +67,11 @@ command-specific flags that are not universally recognized.
 	<https://git.nytpu.com/comitium/about/doc/translating.md> for available
 	options.  Defaults to en-US.
 
+*-h* _DAYS_, *--history* _DAYS_
+	The number of days of articles to display on *feed.gmi*. For instance, if
+	it's set to 7 then only the past week of posts will be displayed or kept in
+	comitium.json. Defaults to 31.
+
 ## REFRESH FLAGS
 
 *-n* _NUM_, *--num-workers* _NUM_
@@ -98,6 +103,10 @@ command-specific flags that are not universally recognized.
 *COMITIUM_DATA*
 	Set the data directory. Equivalent to the *--data* flag.
 
+*COMITIUM_HISTORY*
+	How many days should be included on *feed.gmi*. Equivalent to the
+	*--history* flag.
+
 *LANG*
 	Set the language comitium will output.