Add usage notes

README.md

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-patrix is a simple command line client for Matrix written in perl. It can send text messages to rooms. I use it to send Zabbix alertes to a Matrix room, a bit like sendxmpp can do with XMPP
+patrix is a simple command line client for Matrix written in perl. It can send text messages to rooms. I use it to send Zabbix alertes to a Matrix room, a bit like sendxmpp can do with XMPP.
+
+It requires the following perl modules
+  * LWP::UserAgent
+  * HTTP::Request
+  * Config::Simple
+  * File::HomeDir
+  * Getopt::Long
+  * JSON
+
+For now it's very limited, and can only send messages to a room. Here's the vailable options:
+
+  * --user: specify the user you want to login as
+  * --password: the password to auth against the HS
+  * --server: the HS you want to connect to. Default is https://matrix.org
+  * --access_token: can be used instead of --user and --password
+  * --room: the room to which the message must be sent
+  * --message: the text message you want to send. If you send something on stdin, it's assumed to be the text to send and this option is ignored
+  * --debug: if present, will be verbose
+  * --notice: send a notice instead of a message (more or less the same but the client can display it differently. Riot for example will not notify you for notices)
+  * --conf: path to a conf file. Default conf file is ~/.patrixrc
+  * --action: what to do. Valid actions are
+    * send-msg (default): send the text message
+    * get-access-token: just login and print the access token
+
+All the available options can be set a the configuration file using a simple ini style format, eg
+
+user=alert
+password=p@ssw0rd
+room=!BWdARvAgNQGgSjgtAG:matrix.domain.com