Add README.md with instructions

Author: robertodr

README.md

@@ -0,0 +1,15 @@
+
+Requires at least CMake 3.11
+
+Configure with:
+```
+cmake -H. -Bbuild -DENABLE_OPENMP=ON
+```
+Compile with:
+```
+cmake --build build
+```
+Test run with:
+```
+env OMP_NUM_THREADS=2 OMPYBIND11_MODULE_PATH=$PWD/build/ompybind11 python ompybind11/test.py
+```