Warn if tmp dir is the current working directory

[drshrey]

In .air.conf, if you set the tmp to ".", your entire current working directory will be wiped. This can be very bad especially if you haven't committed to git in a while. Can we have a warning if it is set to "." or atleast some documentation around that please?

My .air.conf that caused this:

# Working directory
# . or absolute path, please note that the directories following must be under root
root = "." 
# Optional! If `watch_dir` is empty, use `root`.
watch_dir = ""
tmp_dir = "."

[build]
# Just plain old shell command. You could use `make` as well.
cmd = "go build"
# Binary file yields from `cmd`.
bin = "main"

[cosmtrek]

Thanks for your advice, it does make sense, I'll update the README.

[musinit]

Maybe show it like this?
#64