Add option to play notification sound.

[akaydesai]

Default behavior is unchanged - does not play notification sound. To change this, set UDM_PLAY_SOUND in bashrc to non-zero value.

[jml]

Thanks! I'm unsure about this change. Could you please document these optional dependencies in the README?

[akaydesai]

I have explained the dependencies in the comments above, and also put in a paragraph in the README under the Configuration section. Alternatively we could remove the sound-theme-freedesktop dependency and provide the sound file in the source tree itself, or let the user select a file themselves. But since most desktop environments usually ship with the two packages installed, adding two tiny dependencies doesn't seem to be a big deal.

[akaydesai]

Covered all the grammar bases. :)

[akaydesai]

Accidentally closed this prematurely.

[jml]

Thanks!