more prominent clippy cross-referencing

[wookietreiber]

Some of the idioms can be checked with clippy, e.g.:

#![deny(clippy::all)]
#![warn(clippy::pedantic, clippy::nursery, clippy::cargo)]

fn mylen(s: String) -> usize {
    s.len()
}

fn mylen2(s: &String) -> usize {
    s.len()
}

fn main() {
    println!("{}", mylen(String::from("foo")));
    println!("{}", mylen2(&String::from("foo")));
}

warning: this argument is passed by value, but not consumed in the function body
 --> examples/borrow.rs:4:13
  |
4 | fn mylen(s: String) -> usize {
  |             ^^^^^^ help: consider changing the type to: `&str`
  |
note: the lint level is defined here
 --> examples/borrow.rs:2:9
  |
2 | #![warn(clippy::pedantic, clippy::nursery, clippy::cargo)]
  |         ^^^^^^^^^^^^^^^^
  = note: `#[warn(clippy::needless_pass_by_value)]` implied by `#[warn(clippy::pedantic)]`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_value

error: writing `&String` instead of `&str` involves a new object where a slice will do
 --> examples/borrow.rs:8:14
  |
8 | fn mylen2(s: &String) -> usize {
  |              ^^^^^^^ help: change this to: `&str`
  |
note: the lint level is defined here
 --> examples/borrow.rs:1:9
  |
1 | #![deny(clippy::all)]
  |         ^^^^^^^^^^^
  = note: `#[deny(clippy::ptr_arg)]` implied by `#[deny(clippy::all)]`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

---

I am advocating for more prominent clippy cross-referencing. This could be in the form of a big box that says something like:

Note: To enforce this idiom in your entire codebase, use #[deny(clippy::needless_pass_by_value)] and #[deny(clippy::ptr_arg)].

I think these note boxes should be added to all applicable idioms. We are all human and tend to miss something at some point. If clippy rules exist that can be used to enforce idioms, they should be prominently highlighted in the respective sections.