Update feature tables

Author: termoshtt

lax/README.md

@@ -10,11 +10,14 @@ This crate responsibles for
 Features
 ---------
 
-| Feature          | Link type      | Description |
-|:-----------------|:---------------|:----------------------------------------|
-| openblas-static  | static         | Build OpenBLAS, and link it statically  |
-| openblas-system  | dynamic/static | Seek OpenBLAS in system (e.g. `/usr/lib/libopenblas.so`), and link it. Shared library (use dynamic linking) is prior to static library (`libopenblas.a`) |
-| netlib-static    | static         | Same as openblas-static except for using reference LAPACK |
-| netlib-system    | dynamic/static | Same as openblas-system except for using reference LAPACK |
-| intel-mkl-static | static         | Seek static library of Intel MKL from system, or download if not found, and link it statically |
-| intel-mkl-system | dynamic        | Seek shared library of Intel MKL from system, and link it dynamically |
+| Feature          | Link type      | Requirements        | Description |
+|:-----------------|:---------------|:--------------------|:----------------------------------------|
+| openblas-static  | static         | gcc, gfortran, make | Build OpenBLAS, and link it statically  |
+| openblas-system  | dynamic/static | -                   | Seek OpenBLAS in system (e.g. `/usr/lib/libopenblas.so`), and link it. Shared library (use dynamic linking) is prior to static library (`libopenblas.a`) |
+| netlib-static    | static         | gfortran, make      | Same as openblas-static except for using reference LAPACK |
+| netlib-system    | dynamic/static | -                   | Same as openblas-system except for using reference LAPACK |
+| intel-mkl-static | static         | (pkg-config)        | Seek static library of Intel MKL from system, or download if not found, and link it statically |
+| intel-mkl-system | dynamic        | (pkg-config)        | Seek shared library of Intel MKL from system, and link it dynamically |
+
+- You must use **just one** feature of them.
+- `pkg-config` is used for searching Intel MKL packages in system, and it is optional. See [intel-mkl-src/README.md](https://github.com/rust-math/intel-mkl-src/blob/master/README.md#how-to-find-system-mkl-libraries) for detail.