document Rust version range that uses OptionExt::contains

[soc]

That is:

• From Rust 1.0 ...
• ... until the unstable method was added to std (shipped in 1.37.0, so 1.36.0 probably) ...
• ... and then perhaps in future versions of Rust again, depending on the outcome of the intellectual tire fire in Tracking issue for Option::contains and Result::contains rust-lang/rust#62358.

[soc]

→ I got the functions removed in rust-lang/rust#108095.

[soc]

With rust-lang/rust#62358 closed, this means that OptionExt::contains can now be used without being hassled by CLion.