Add changelog entry

CHANGELOG.rst

 This document contains the FSL-MRS release history in reverse chronological order.
 
+1.1.6 (WIP)
+-----------
+- Updates to dynamic MRS fitting in prep for dwMRS workshop.
+
 1.1.5 (Wednesday 11th August 2021)
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 - Updated example MRSI data to conform to NIfTI-MRS standard.