update release notes

RELEASE-NOTES

@@ -1,7 +1,19 @@
 GFAL2 RELEASE-NOTES
 ===================
+## Mon May 28 2018 Andrea Manzi <amanzi at cern.ch> - 2.15.5
+### Bug
+- [DMC-1023] - Xrootd plugin:The checksum string provided by the user is not correctly parsed
+- [DMC-1041] - Incorrect GridFTP listing output
+
+### Improvement
+- [DMC-1036] - gfal_http_get_token should read the credentials associated to the host
+
+### New Feature
+- [DMC-1038] - Implement abort files for Xrootd bringonline
+- [DMC-1040] - Xrootd plugin: implement the query for the EOS-CTA extended attribute 'sys.retrieve.error'
+
 ## Thu Apr 05 2018 Andrea Manzi <amanzi at cern.ch> - 2.15.4
-#### Bug
+### Bug
 - [DMC-1027] - DAVIX operation timeout incorrect for HTTP-based transfers 
 - [DMC-1031] - gfal_http_get_token does not free the gchar* token
 - [DMC-1034] - When ENABLE_STREAM_COPY is disabled the http copy process crashes