Add build version reporting

docs/cli.md

@@ -10,6 +10,7 @@ defined in [Operations](operations.md).
 
 ~~~
 notarius help
+notarius --version
 notarius run <pipeline-id> --input path/to/source.json [--json] [flags]
 notarius config validate [--config path/to/config.yml] [--pipeline pipeline-id] [--only lane-a,lane-b]
 notarius pipelines list [--config path/to/config.yml] [--json]
@@ -18,6 +19,17 @@ notarius pipelines list [--config path/to/config.yml] [--json]
 Running Notarius without arguments, or with **help**, **--help**, or **-h**,
 writes the command summary to standard output and exits with status 0.
 
+`notarius --version` is valid only as the sole root argument. It writes exactly
+`notarius <version>` followed by a newline to standard output and exits with
+status 0. A tagged `go install` build can report its main-module stable tag,
+and controlled builds can inject a stable tag at link time through
+`gitea.maximumdirect.net/eric/notarius/internal/buildinfo.Override`; an ordinary
+unversioned checkout reports `development`. Invalid injected version content is
+a runtime error with exit status 1, while extra `--version` arguments are a
+syntax error with exit status 2. This diagnostic does not replace the
+[run-result](integrations/run-result.md) or artifact contracts for downstream
+compatibility decisions.
+
 ## run
 
 ~~~