chore(docs): CLI release train command added to documentation (#1907)

Ref: SRX-L4NJ07

docs/release-train.md

@@ -38,6 +38,26 @@ or
 * `team=${myTeam}` is an optional parameter. If set, the release train will only apply for
 [apps](./app.md) that have exactly the give team set in the [`/release` endpoint](./release.md)
 
+### CLI
+
+There is a Kubepult command line client for communicating with the `/release-train` endpoint now at [`cli`](https://github.com/freiheit-com/kuberpult/tree/main/cli). The usage is as follows:
+
+```
+kuberpult-client --url=${kuberpult_URL} \
+    release-train \
+    --target-environment=staging \
+    --team=sre-team
+```
+
+The flags:
+```
+  -target-environment value
+    	the name of the environment to target with the release train (must be set exactly once)
+  -team value
+    	the target team. Only specified teams services will be taken into account when conducting the release train
+  -use_dex_auth
+    	if set to true, the /api/* endpoint will be used. Dex must be enabled on the server side and a dex token must be provided, otherwise the request will be denied
+```
 
 ### Prognosis