Improve README

- Update dependency versions to those of Debian Buster
- link to bug tracker
- fix minor formatting issues

README.md

@@ -1,4 +1,4 @@
-# check_xmppng - check plugin for XMPP
+# `check_xmppng` - check plugin for XMPP
 
 This program implements a nagios check plugin for XMPP servers implementing the
 XMPP protocol as specified in [RFC 6120](http://tools.ietf.org/html/rfc6120).
@@ -10,8 +10,9 @@ The program implements the following features:
 * support STARTTLS as specified in RFC 6120 section 5.
 * check the validity of the server certificate presented by the XMPP server
 
-The plugin has been implemented because of insufficiencies in check_ssl_cert
-and the existing [check_xmpp](https://exchange.icinga.org/exchange/check_xmpp).
+The plugin has been implemented because of insufficiencies in `check_ssl_cert`
+and the existing
+[`check_xmpp`](https://exchange.icinga.org/exchange/check_xmpp).
 
 Maximum acceptable timeouts as well as minimum acceptable number of days the
 server certificate needs to be valid can be specified as command line
@@ -30,14 +31,14 @@ the Python standard library:
 
 The software has been developed and tested with the following versions:
 
-* Python 3.4.2
-* defusedxml 0.4.1
-* nagiosplugin 1.2.2
+* Python 3.7.3
+* defusedxml 0.5.0
+* nagiosplugin 1.2.4
 
 
 ## License
 
-check_xmppng is free software: you can redistribute it and/or modify it under
+`check_xmppng` is free software: you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
 Foundation, either version 3 of the License, or (at your option) any later
 version.
@@ -95,5 +96,6 @@ optional arguments:
 
 ## Contact
 
-If you want to provide feedback or bug reports please send me a mail to
-jan (at) dittberner [dot] info.
+If you want to provide feedback or bug reports please use the [bug
+tracker](https://git.dittberner.info/jan/check_xmppng/issues) or send me an
+email to jan (at) dittberner [dot] info.