update release notes

RELEASE_NOTES.txt

+Release 3.0.0 (07/26/2019)
+=============================
+- Added python web service API for downloading files 
+- Updated DB schema for experiment data archival support
+- Web Portal changes:
+  - Added storage views
+  - Added connection between station and experiment types
+  - Updated experiment views with storage and root path fields
+
 Release 2.6.0 (07/15/2019)
 =============================
 - Moved code repo to gitlab