Update docs regarding deploy chatops slash command

doc/integration/slash_commands.md

@@ -2,7 +2,11 @@
 
 Slash commands in Mattermost and Slack allow you to control GitLab and view GitLab content right inside your chat client, without having to leave it. For Slack, this requires a [project service configuration](../user/project/integrations/slack_slash_commands.md). Simply type the command as a message in your chat client to activate it.
 
-Commands are scoped to a project, with a trigger term that is specified during configuration. (We suggest you use the project name as the trigger term for simplicty and clarity.) Taking the trigger term as `project-name`, the commands are:
+Commands are scoped to a project, with a trigger term that is specified during configuration.
+
+We suggest you use the project name as the trigger term for simplicity and clarity.
+
+Taking the trigger term as `project-name`, the commands are:
 
 
 | Command | Effect |
@@ -12,3 +16,18 @@ Commands are scoped to a project, with a trigger term that is specified during c
 | `/project-name issue show <id>` | Shows the issue with id `<id>` |
 | `/project-name issue search <query>` | Shows up to 5 issues matching `<query>` |
 | `/project-name deploy <from> to <to>` | Deploy from the `<from>` environment to the `<to>` environment |
+
+## Issue commands
+
+It is possible to create new issue, display issue details and search up to 5 issues.
+
+## Deploy command
+
+In order to deploy to an environment, GitLab will try to find a deployment
+action in the pipeline.
+
+If there is only one action for a given environment, it is going to be triggered.
+If there is more than one action defined, GitLab will try to find an action
+which name equals the environment name we want to deploy to.
+
+Command will return an error when no matching action has been found.