update README

README.md

@@ -8,17 +8,27 @@ How to build and debug the library during development.
 
 ### Prerequisites
 The following packages are required in order to build the library:
-* cmake 3.8+
+* C++:
+  * cmake 3.8+
   * gcc 7+/clang 7+/msvc 16+
   * fmtlib 5.2.1+
   * pybind11 2.3.0+
-* python 3.6+
+* Python:
+  * python 3.6+
   * setuptools
-  * wheel
   * pybind11
   * numpy
   * pyside2/pyqt5
 
+To build a binary distribution, the following additional packages are required:
+* Python:
+  * wheel
+
+To run the test suite, the following additional packages are required:
+* Python:
+  * pytest
+  * pytest-cov (for testing with coverage)
+
 ### Using CMake directly
 How to build using CMake.