#24 Add Link to Thunderbird Promotional Flyer

[Nathan]

The CD contains a promotional flyer for Thunderbird
[\src\firemonger\content\resources\thunderbird\Thunderbird-Flyer-a-A4.en-us.pdf).

However, it seems that it isn't linked from the
promotional section on the CD. We should incorporate a
link to it, or else delete the pdf file.

While we're at it, we can improve the flyer (e.g. add
background graphics, make look more appealing).

[pdf file attached for easy inspection]

[Nathan]

Thunderbird Promotional Flyer