added release notes

Author: sy-c

doc/releaseNotes.md

@@ -0,0 +1,8 @@
+# ReadoutCard release notes
+
+This file describes the main feature changes for released versions of ReadoutCard library and tools.
+
+## v0.38.0 - 05/09/2022
+- Added release notes as part of source code.
+- Added library version number. Can be retrieved at runtime with o2::roc::getReadoutCardVersion().
+- Fixed bug in DMA reset. Old data from previous run could stay in the pipeline if previous process was stopped abruptly.