[modules/*] Add required executables/commandline tools to help output

fixes #39

bumblebee/modules/brightness.py

@@ -2,8 +2,12 @@
 
 """Displays the brightness of a display
 
+Requires the following executable:
+    * xbacklight
+
 Parameters:
     * brightness.step: The amount of increase/decrease on scroll in % (defaults to 2)
+
 """
 
 import bumblebee.input

bumblebee/modules/caffeine.py

@@ -1,6 +1,10 @@
 # pylint: disable=C0111,R0903
 
 """Enable/disable automatic screen locking.
+
+Requires the following executables:
+    * xset
+    * notify-send
 """
 
 import bumblebee.input

bumblebee/modules/cmus.py

@@ -2,6 +2,9 @@
 
 """Displays information about the current song in cmus.
 
+Requires the following executable:
+    * cmus-remote
+
 Parameters:
     * cmus.format: Format string for the song information. Tag values can be put in curly brackets (i.e. {artist})
 """

bumblebee/modules/dnf.py

@@ -2,6 +2,9 @@
 
 """Displays DNF package update information (<security>/<bugfixes>/<enhancements>/<other>)
 
+Requires the following executable:
+    * dnf
+
 Parameters:
     * dnf.interval: Time in seconds between two consecutive update checks (defaulst to 1800)
 

bumblebee/modules/gpmdp.py

@@ -2,6 +2,8 @@
 
 """Displays information about the current song in Google Play music player.
 
+Requires the following executable:
+    * gpmdp-remote
 """
 
 import string

bumblebee/modules/layout.py

@@ -2,6 +2,9 @@
 
 """Displays and changes the current keyboard layout
 
+Requires the following executable:
+    * setxkbmap
+
 Parameters:
     * layout.lang: pipe-separated list of languages to cycle through (e.g. us|rs|de). Default: en
 """

bumblebee/modules/pacman.py

@@ -1,6 +1,10 @@
 # pylint: disable=C0111,R0903
 
 """Displays update information per repository for pacman."
+
+Requires the following executables:
+    * fakeroot
+    * pacman
 """
 
 import os

bumblebee/modules/ping.py

@@ -2,6 +2,9 @@
 
 """Periodically checks the RTT of a configurable host using ICMP echos
 
+Requires the following executable:
+    * ping
+
 Parameters:
     * ping.interval: Time in seconds between two RTT checks (defaults to 60)
     * ping.address : IP address to check

bumblebee/modules/pulseaudio.py

@@ -3,6 +3,9 @@
 """Displays volume and mute status of PulseAudio devices.
 
 Aliases: pasink, pasource
+
+Requires the following executable:
+    * pactl
 """
 
 import re

bumblebee/modules/xrandr.py

@@ -2,6 +2,8 @@
 
 """Shows a widget for each connected screen and allows the user to enable/disable screens.
 
+Requires the following executable:
+    * xrandr
 """
 
 import os