doc: improve pmt/pmtx manual pages

docs/pmtx/description.rst

@@ -1,6 +1,3 @@
-Description
-^^^^^^^^^^^
-
 The ``pmtx`` command controls SCSI media changer devices (tape
 autoloader).
 

docs/pmtx/man1.rst

@@ -18,11 +18,40 @@ Synopsis
 
 .. include:: synopsis.rst
 
+
+Common Options
+==============
+
+All command supports the following parameters to specify the changer device:
+
+--device <path>  Path to Linux generic SCSI device (e.g. '/dev/sg4')
+
+--changer <name>  Use changer from Proxmox Backup Server configuration.
+
+
+Commands generating output supports the ``--output-format``
+parameter. It accepts the following values:
+
+:``text``: Text format (default). Human readable.
+
+:``json``: JSON (single line).
+
+:``json-pretty``: JSON (multiple lines, nicely formatted).
+
+
 Description
 ============
 
 .. include:: description.rst
 
 
-.. include:: ../pbs-copyright.rst
+ENVIRONMENT
+===========
 
+:CHANGER: If set, replaces the `--device` option
+
+:PROXMOX_TAPE_DRIVE: If set, use the Proxmox Backup Server
+   configuration to find the associcated changer device.
+
+
+.. include:: ../pbs-copyright.rst