Feat: add an error message when WTF was failed

[flw-cn]

This is just a minor change to avoid a small number of inexperienced
users not be intimidated by a minor mistake, such as the incorrect
setting of the TERM environment variable.

I hope this will be improved a bit of user experience for let WTF
more popular.

[senorprogrammer]

This looks like a great addition. What should I do to trigger it so I can see it execute in action?

[evanfoster]

Speaking from experience, this causes the problem:

TERM=xterm-termite ./wtf

Glad I saw this! My $TERM var is set to xterm-termite and I was beating my head against the wall trying to get this thing to work. Doing this:

TERM=xterm-256color ./wtf

Made wtf start up. I don't know if this is in the docs (I looked and couldn't find it) but if it isn't you might want to mention acceptable values for $TERM.

[senorprogrammer]

Great idea. Will add to docs at some point.

[senorprogrammer]

This commit 7545ead might be of interest to you. You can now specify the terminal type in your config file.