better installation instructions

Makefile

@@ -1,12 +1,18 @@
+# The C++ compiler. Adjust if needed
 CXX:=g++
 
+# python-config tool.
+PYTHON_CONFIG:=python-config
+
+
+
 PYETS_DEP:=src/ets.cc src/pyETS.cc src/*.h src/external/*
 PYETS_SRC:=src/ets.cc src/pyETS.cc src/external/*.cc
 PYCCONV_DEP:=src/cconv.cc src/pycconv.cc src/*.h src/external/*
 PYCCONV_SRC:=src/cconv.cc src/pycconv.cc src/external/*.cc
 
 PYBIND_INC:=src
-PYFLAGS:=$(filter-out -Wstrict-prototypes,$(shell python-config --cflags --ldflags))
+PYFLAGS:=$(filter-out -Wstrict-prototypes,$(shell $(PYTHON_CONFIG) --cflags --ldflags))
 
 COMMON_FLAGS:=-O3 -g -fmax-errors=1 -std=c++14 -I src/external -W -Wall
 

README.md

@@ -18,6 +18,14 @@ Pybind11 headers for C++/Python integration
 Simply type "make". This requires a fairly recent version of GNU g++ (tested
 with version 5.3 and above, but any 5.x will probably work).
 
+If you can compile the code but you get error messages when trying to import
+the Python modules, chances are that the "python" executable and the Python
+configuration tool "python-config" in your search path don't match; this
+can happen when installing a new Python interpreter from a software repository
+in addition to the one distributed with the system. In this case you can edit
+the Makefile and set the PYTHON_CONFIG variable to the appropriate
+"python-config" with full path.
+
 ## Demo code:
 
 The file demo.py contains a very brief overview over the typical workflow, i.e.