Message suggesting --allow-dirty should clearly specify what will happen when it is specified

[nagisa]

Problem

When publishing with dirty files in tree cargo prints a message:

error: 2 files in the working directory contain changes that were not yet committed into git:

out
src/os/unix/global_static.ll

to proceed despite this, pass the `--allow-dirty` flag

however it does not specify what will happen if --allow-dirty is specified. It should unambiguously mention that specifying this flag will include the dirty files.

Possible Solution(s)

to proceed despite this and include the dirty files, pass the --allow-dirty flag