README: Add requirements for compression libraries.

Signed-off-by: Grzegorz Kowal <grzegorz@amuncode.org>

README.md

@@ -60,6 +60,10 @@ Requirements
       compiler version 9.0 or newer.
 * Optional, but recommended, [OpenMPI](https://www.open-mpi.org/) for parallel
   runs, tested with version 1.8 or newer.
+* Optional support for XML-binary format compression requires:
+  [LZ4 library](https://lz4.github.io),
+  [Zstandard library](http://facebook.github.io/zstd/), or
+  [LZMA library](https://tukaani.org/xz/)
 * Optional [HDF5 libraries](https://www.hdfgroup.org/solutions/hdf5/), tested
   with version 1.10 or newer. The code now uses the new XML-binary snapshot
   format. However, if you still want to use older HDF5 snapshot format, you