docs: further updates to 2.16.x What's New (pantsbuild#18227)

Add more updates for 2.16.x to the What's New section.

src/python/pants/notes/2.16.x.md

@@ -2,7 +2,23 @@
 
 ## What's New
 
-### Go
+### BUILD files
+
+The new `env` function in BUILD files allows access to environment variables in BUILD files.
+
+### Backends
+
+#### Python
+
+The Python backend has two new linters:
+
+[`pydocstyle`](https://www.pydocstyle.org/) is now supported for linting Python doc strings. Enable the
+`pants.backend.python.lint.pydocstyle` backend to add this support.
+
+[`ruff`](https://github.com/charliermarsh/ruff) is now supported for linting and formatting Python code. Enable the
+`pants.backend.experimental.python.lint.ruff` backend to add this support.
+
+#### Go
 
 The Go backend has received a large number of changes in order to be ready for Go v1.20
 and to make continued progress on [stabilizing the Go backend](https://github.com/pantsbuild/pants/issues/17447).
@@ -16,6 +32,32 @@ apply compiler options consistently when building Go SDK packages.)
 The Pants team would appreciate if the community could try out 2.16.x with your Go code as an additional
 check to ensure there are no regressions.
 
+The Go backend also now supports:
+- Environments are supported via the `environment` field available now on `go_binary` targets.
+- Code coverage can now analyze coverage for packages beyond just the package under test via the new
+`--go-test-cover-packages` option.
+- Numerous bug fixes to the Cgo support.
+- Race detector is supported via the `race` field now available on `go_binary` targets.
+- Compiler and other flags may be set via the `compiler_flags`, `linker_flags`, and `assembler_flags` fields
+available on various target types.
+
+#### Shell
+
+A new `experimental_test_shell_command` target type has been added to allow defining arbitrary shell commands
+as tests which can be invoked using the `./pants test` goal.
+
+`experimental_shell_command` now supports the `environment` field for running in non-local environments.
+
+#### New: Preamble
+
+The new "preamble" plugin allows linting files to ensure they start with specific text. Enable the
+`pants.backend.tools.preamble` backend to add this support.
+
+#### New: CUE
+
+Pants now supports the [CUE language](https://cuelang.org/) for defining, generating, and validating configuraton data.
+Enable the `pants.backend.experimental.cue` backend to add this support.
+
 ## 2.16.0.dev6 (Jan 29, 2023)
 
 ### New Features