Move 3.8.1 release notes to master branch.
Move 3.8.1 release notes to master branch.

This should have been included in the master before being backported

umar456/arrayfire,9prady9/arrayfire,9prady9/arrayfire,arrayfire/arrayfire,umar456/arrayfire,arrayfire/arrayfire,umar456/arrayfire,arrayfire/arrayfire,umar456/arrayfire,9prady9/arrayfire,arrayfire/arrayfire,9prady9/arrayfire