chore: mark code snippet in README.md no_run

[kaspar030]

Fixes this clippy warning:

warning: unit tests in doctest are not executed
   --> src/../README.md:108:5
    |
108 |     #[test]
    |     ^^^^^^^
...
114 |     #[test]
    |     ^^^^^^^
...
123 |     #[test]
    |     ^^^^^^^
...
130 |     #[test]
    |     ^^^^^^^
...
136 |     #[test]
    |     ^^^^^^^
...
143 |     #[test]
    |     ^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.94.0/index.html#test_attr_in_doctest
    = note: `#[warn(clippy::test_attr_in_doctest)]` on by default