add release note file

RELEASE_NOTES.md

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+# PnetCDF-Python Release Notes
+
+### Version 1.0.0 (September 12, 2024)
+
+* First release of PnetCDF-Python package, a Python interface to PnetCDF-C
+  parallel I/O library.
+* User Guide is provided in https://pnetcdf-python.readthedocs.io/en/latest
+* A high-level comparison between PnetCDF and NetCDF4 is described in
+  file `docs/nc4_vs_pnetcdf.md`
+* Several python example programs are available in folder `examples`.
+* Source codes are stored in its github repository at
+  https://github.com/Parallel-NetCDF/PnetCDF-Python
+
+