Renamed src/README.md to src/.BUILD_LOCALLY.md

Provided more context to the command stated in the readme, and
changed so as to not hard-code installation paths of NVBench,
and checkout path of pybind11.

Author: oleksandr-pavlyk

python/src/.BUILD_LOCALLY.md

@@ -0,0 +1,24 @@
+# Building extension module locally
+
+This may be useful for debugging purposes.
+Assuming NVBench is installed into `NVBENCH_PREFIX`,
+and pybind11 repo is cloned to `PYBIND11_DIR`,
+Python extension can be built locally, using host compiler,
+as follows:
+
+```bash
+g++ py_nvbench.cpp                                  \
+   -shared -fPIC                                    \
+   -I ${PYBIND11_DIR}/include                       \
+   -I ${NVBENCH_PREFIX}/include                     \
+   -I /usr/local/cuda/include                       \
+   $(python3-config --includes)                     \
+   $(python3-config --libs)                         \
+   -L ${NVBENCH_PREFIX}/lib/                        \
+   -lnvbench                                        \
+   -Wl,-rpath,${NVBENCH_PREFIX}/lib                 \
+   -L /usr/local/cuda/lib64/                        \
+   -lcudart                                         \
+   -Wl,-rpath,/usr/local/cuda/lib64                 \
+   -o _nvbench$(python3-config --extension-suffix)
+```