Add a link to the usage page

Author: IvanUkhov

README.md

@@ -1,6 +1,7 @@
 # LAPACK [![Package][package-img]][package-url] [![Documentation][documentation-img]][documentation-url] [![Build][build-img]][build-url]
 
-The package provides wrappers for [LAPACK] (Fortran).
+The package provides wrappers for [LAPACK] (Fortran). The usage of the package
+is explained [here][usage].
 
 ## Example
 
@@ -31,6 +32,7 @@ pull request. Note that any contribution submitted for inclusion in the project
 will be licensed according to the terms given in [LICENSE.md](LICENSE.md).
 
 [lapack]: https://en.wikipedia.org/wiki/LAPACK
+[usage]: https://blas-lapack-rs.github.io/usage
 
 [build-img]: https://travis-ci.org/blas-lapack-rs/lapack.svg?branch=master
 [build-url]: https://travis-ci.org/blas-lapack-rs/lapack

src/lib.rs

@@ -1,5 +1,7 @@
 //! Wrappers for [LAPACK] \(Fortran)
 //!
+//! The usage of the package is explained [here][usage].
+//!
 //! ## Example
 //!
 //! ```no_run
@@ -23,6 +25,7 @@
 //! ```
 //!
 //! [lapack]: https://en.wikipedia.org/wiki/LAPACK
+//! [usage]: https://blas-lapack-rs.github.io/usage
 
 extern crate lapack_sys as ffi;
 extern crate libc;