message: add "known issues" section to changelog
diff: @@ -55,6 +55,16 @@ Version History
  - Expansion of information returned by `ospPick`
  - Addition of API to query version information at runtime
  +- Known issues:
  + - Open VKL must be built with a compatible set of ISAs with OSPRay
  + due to a known issue with VKL iterator types. This is easiest
  + to address by using `OSPRAY_BUILD_ISA` and `OPENVKL_BUILD_ISA`
  + with the ISA of the target machine. This will be addressed for
  + the official v2.0 release.
  + - The old variant of `ospNewData` was temporarily retained in
  + `ospray_util.h` for C++ applications and will be removed for the
  + official v2.0 release
  +
  ### Changes in v1.8.5:
  - Fix float precision cornercase (`NaN`s) in sphere light sampling
  