add `abi_x86_interrupt` to the unstable book

[steveklabnik]

see #40180

I'm happy to help mentor anyone who wants to fix this issue.

[topecongiro]

Hello, I would like to work on this issue.

[jdhorwitz]

I would love to work on this and be mentored as well in case topecongiro can not. Thank you!

[steveklabnik]

@jdhorwitz #40191 got sent in, so maybe we can work together on some other issue? 😄 Just let me know, happy to help you help me.

[jdhorwitz]

@steveklabnik That would be great, thank you so much would love to work with you.

[steveklabnik]

@jdhorwitz Awesome. Maybe jump on IRC and message me? Or comment in another issue marked E-mentor? Whatever works 👍

[jdhorwitz]

@steveklabnik Awesome! What is your nick on IRC? Mine is jhorwitz

[steveklabnik]

same as github: steveklabnik