Update changelog with memory change

CHANGELOG.md

@@ -9,6 +9,11 @@ that users understand how the changes affect the new version.
 -->
 version 5.1.0-dev
 ---------------------------
++ Move all memory notation to `KiB`, `MiB` and `GiB` from `K`, `M` and `G` 
+  previously. The WDL spec clearly distuingishes between SI and binary 
+  notations. Since Java always takes `K`, `M` and `G` to mean `KiB`, `MiB` and 
+  `GiB` this means java tasks such as GATK, FastQC and Picard will always 
+  receive enough memory now.  
 + Purple's `somaticRainfallPlot` output is now optional and included in
   the `plots` output as well.
 + Bedtools coverage's timeMinutes now defaults to `320`.