Fix CMake installation instructions in LAPACK README

The `CMAKE_INSTALL_LIBDIR` was used here from the command line, probably
accidentally. It is a variable provided by the core CMake module
GNUInstallDirs and shouldn't be overridden. The variable, that makes
sense in this context is the `CMAKE_INSTALL_PREFIX` variable, which is
intended to be set by the user.

Author: lepus2589

README.md

@@ -79,7 +79,7 @@ CBLAS, a C interface to the BLAS, and (5) LAPACKE, a C interface to LAPACK.
    ```sh
    mkdir build
    cd build
-   cmake -DCMAKE_INSTALL_LIBDIR=$HOME/.local/lapack ..
+   cmake -DCMAKE_INSTALL_PREFIX=$HOME/.local/lapack ..
    cmake --build . -j --target install
    ```
  - LAPACK can be built and installed using [vcpkg](https://github.com/Microsoft/vcpkg/) dependency manager: