Updated release notes with information regarding #159.

Author: WardF

RELEASE_NOTES.md

@@ -7,6 +7,8 @@ This file contains a high-level description of this package's evolution. Release
 
 ## 4.4.0 Released TBD
 
+* Addressed an issue on platforms where `char` is `unsigned` by default (such as `ARM`), as well as an issue describing regarding undefined behavior, again on `ARM`.  See [GitHub issue #159](https://github.com/Unidata/netcdf-c/issues/159) for detailed information.
+
 * Modified ncgen to properly handle the L and UL suffixes for integer constants
   to keep backward compatibility. Now it is the case the single L suffix
   (e.g. 111L) is treated as a 32 bit integer. This makes it consistent with