update release notes

RELEASE_NOTES.txt

-Release 2.0.1 (MM/DD/2018)
+Release 2.1.0 (MM/DD/2018)
 =============================
 - Added estimated completion time to upload monitoring
+- Introduced additional enhancements for cataloging plugin that shorten
+  uploads of large datasets
+- Developed initial image receiver service and utilities that can accept
+  Area Detector NTNDArray frames and save them into files; currently
+  supported formats are SDDS, JSON, HDF5, and JPEG.
+  
 
 Release 2.0.0 (10/15/2018)
 =============================