cmdmon: add reload sources command

Add the command which reloads the files from the directories specified
by the sourcedirs directive.

doc/chrony.conf.adoc

@@ -2152,8 +2152,12 @@ confdirs @SYSCONFDIR@/chrony.d /var/run/chrony.d /usr/lib/chrony.d
 
 [[sourcedirs]]*sourcedirs* _directory_...::
 The *sourcedirs* directive is identical to the *confdirs* directive, except the
-configuration files have the _.sources_ suffix and they can only specify NTP
-sources (i.e. use the *server*, *pool*, and *peer* directive).
+configuration files have the _.sources_ suffix, they can only specify NTP
+sources (i.e. use the *server*, *pool*, and *peer* directive), and can be
+reloaded by the <<chronyc.adoc#reload,*reload sources*>> command in
+*chronyc*. It is particularly useful with dynamic sources like NTP servers
+received from a DHCP server, which can be written to a file specific to the
+network interface by a networking script.
 +
 An example of the directive is:
 +

doc/chronyc.adoc

@@ -928,6 +928,11 @@ Sources that stop responding will be replaced with newly resolved addresses
 automatically after 8 polling intervals, but this command can still be useful
 to replace them immediately and not wait until they are marked as unreachable.
 
+[[reload]]*reload* *sources*::
+The *reload sources* command causes *chronyd* to re-read all _*.sources_ files
+from the directories specified by the
+<<chrony.conf.adoc#sourcedirs,*sourcedirs*>> directive.
+
 [[sourcename]]*sourcename* _address_::
 The *sourcename* command prints the original hostname or address that was
 specified for an NTP source in the configuration file, or the *add* command.