Update NEWS before 0.6.4 release.

4 jobs for v0.6.4 in 6 minutes and 31 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
passed #294921
build_cran

00:03:53

passed #294920
build_markdown_v1

00:05:30

passed #294923
build_version_devel

00:06:31

passed #294922
build_version_latest

00:03:10