Fixup top-of-module example
Fixup top-of-module example

Use example from README in the top-of-module rust-doc. Also, change the
example from "rust,ignore" to "no_run" so that code is checked for
compile problems.

Signed-off-by: Nick Stevens <75ef9faee755c70589550b513ad881e5a603182c@bitcurry.com>

marjakm/rust-sysfs-gpio,rust-embedded/rust-sysfs-gpio,jwilm/rust-sysfs-gpio,nastevens/rust-sysfs-gpio