Add deploy command doc (#15402)

* docs: add deploy command doc

* docs: fix json example

* docs: add link to cli builder doc

* docs: remove link

* docs: restore link

packages/angular/cli/commands/deploy-long.md

@@ -1,9 +1,22 @@
-The `ng deploy` command is a shortcut for:
+The command takes an optional project name, as specified in the `projects` section of the `angular.json` workspace configuration file.
+When a project name is not supplied, executes the `deploy` builder for the default project.
 
-```
-ng run [PROJECT_NAME]:deploy
-```
+To use the `ng deploy` command, use `ng add` to add a package that implements deployment capabilities to your favorite platform.
+Adding the package automatically updates your workspace configuration, adding a deployment
+[CLI builder](guide/cli-builder).
+For example:
 
-It takes an optional project name, as specified in the `projects` section of the `angular.json` workspace configuration file.
-
-When a project name is not supplied, the CLI will execute the `deploy` builder for the default project.
+```json
+"projects": {
+     "my-project": {
+         ...
+        "architect": {
+            ...
+            "deploy": {
+                "builder": "@angular/fire:deploy",
+                "options": {}
+                }
+            }
+        }
+    }
+ ```

packages/angular/cli/commands/deploy.json

@@ -1,7 +1,7 @@
 {
   "$schema": "http://json-schema.org/schema",
   "$id": "ng-cli://commands/deploy.json",
-  "description": "Invokes the deploy builder for a specified project. If no project is specified, the CLI will invoke the deploy builder for the default project in the workspace.",
+  "description": "Invokes the deploy builder for a specified project or for the default project in the workspace.",
   "$longDescription": "./deploy-long.md",
 
   "$aliases": [ "d" ],