Docs need updating for 128 bit Ints

Learning Resources
1

API docs: https://crystal-lang.org/api/0.35.1/
contains info on 128 bit ints: https://crystal-lang.org/api/0.35.1/Int128.html

but in ref manual: https://crystal-lang.org/reference/
no mention of 128 bit ints:
https://crystal-lang.org/reference/syntax_and_semantics/literals/integers.html

2

I made a PR: https://github.com/crystal-lang/crystal-book/pull/413

3

128-bit literals are not mentioned because they don’t work correctly. See my comment on the PR for details.
Using Int128 and UInt128 is supported in stdlib, but the compiler currently can’t really parse literals.