Hi, all

I'm new to free software community and I'm bit confused about gcc's mirror
repository in github.

It's mirrored from gnu, but there are still pull requests, some are open,
some are closed. What are these PRs, and can I also contribute to
gcc/libgc++ by opening a PR, other than the way suggested here: Contributing
to GCC - GNU Project <https://gcc.gnu.org/contribute.html>, since I don't
understand how to send patch by email.

Thanks for answers and instructions in advance.