Follow up on #269

[panayang]

I see issue #269 has been opened for more than 5 years and thinks it might got forgotten. And after a quick look at the rust nomicon, i think it may need to get some supplement:

• miri (and our two stack models)
• unsafe working group / code guidelines
• Unions
• const and undefined behavior
• ASAN, valgrind, rr, lldb, ci/cd,etc (may be a new tools section for it?)
• Use in real world tips (documentation, commenting, macros, tools (cargo-gieger, cargo-fuzz, kani, loom, proptest), CI)
• GATs (as we already have talked about HRTBs)
• unwinding on windows (TIB/TEB/SEH)
• update the section about thread::scoped::JoinGuard to include the modern version of that api to introduce how to use closures to provide stricter control over lifetimes
• restructure the FFI chapter to make it more well organized
• the beneath the std chapter may need to be hugely improved because there are many danger and many arts there but we now only talked about the panic handler
• a section about inline asm, naked asm and global asm---as they are now stable but really 'unsafe'
• more about async and unsafe---rust has not finish the design works for now, and many devs might write unsafe code
• maybe some note about cross platform problems like alignment and different memory models, too
• other new features of rust recently

And personally I would be glad to help if there is anything i can do. But firstly, we may hope that our maintenance team (t-doc) would decide if these are acceptable goals.
@JohnTitor @ehuss