Add a few doc examples for `std::ffi::OsStr`.
Add a few doc examples for `std::ffi::OsStr`.

* `std::ffi::OsStr::new`.
* `std::ffi::OsStr::is_empty`.
* `std::ffi::OsStr::len`.

graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust