add zenodo.json

Remove included PSRDada sources

now depends again on an external installation of PSRDada

 * set LD_LIBRARY_PATH to point to libpsrdada.so directory; LD_LIBARY_PATH
can be the usual colon separated list
 * add include paths as -I$PATH to CFLAGS, or add paths colon separated to
CFLAGS.

Add co-authors