strings3: Readme.md doesn't provide enough links

[d-patyk]

It only provides a link to the book, which has no mention of .trim and .replace methods.

Should https://doc.rust-lang.org/std/primitive.str.html and possibly https://doc.rust-lang.org/std/string/struct.String.html also be included?

[krishnakumar1723]

Hi, I’d like to improve the documentation links for this issue.