message: fix: Clarify test name filter usage
  Set aside description of the usage example in the top description section and added a more consise example in the example section at the bottom of the man page.
diff: @@ -21,8 +21,10 @@ dashes (`--`) are passed to the test binaries and thus to _libtest_ (rustc's
  built in unit-test and micro-benchmarking framework). If you're passing
  arguments to both Cargo and the binary, the ones after `--` go to the binary,
  the ones before go to Cargo. For details about libtest's arguments see the
  -output of `cargo test \-- --help`. As an example, this will run all tests with
  -`foo` in their name on 3 threads in parallel:
  +output of `cargo test \-- --help`.
  +
  +As an example, this will filter for tests with `foo` in their name and run them
  +on 3 threads in parallel:
  cargo test foo -- --test-threads 3
  @@ -152,6 +154,10 @@ include::section-exit-status.adoc[]
  cargo test
  +. Run only tests whose names match against a filter string:
  +
  + cargo test name_filter
  +
  . Run only a specific test within a specific integration test:
  cargo test --test int_test_name -- modname::test_name
  