Improve syntax highlighting of code snippet.
@@ -14,7 +14,7 @@ performs its own [toolchain resolution](toolchains.md#toolchain-resolution).
To use Starlark rules that create execution groups, set
`--experimental_exec_groups=true` on your command line or in a .bazelrc:
-```
+```shell
$ bazel build //target/with/exec/group --experimental_exec_groups
```
