docs(hub): add description about the tag of hub (#3125)

.github/2.0/cookbooks/Hub.md

@@ -86,6 +86,14 @@ $ jina hub push <path_to_executor_folder> -t TAG1 -t TAG2 -f <path_to_dockerfile
 
 You can specify `-t` or `--tags` parameters to tag one Executor. In additional, you can specify `-f` or `--docker-file` parameters to use a specific docker file to build your Executor.
 
+If there is no `-t` parameter provided, the default tag is `latest`. And if you provide `-t` parameters, and you still want to have `latest` tag, you must write it as one `-t` parameter.
+
+```bash
+$ jina hub push .                     # Result in one tag: latest
+$ jina hub push . -t v1.0.0           # Result in one tag: v1.0.0
+$ jina hub push . -t v1.0.0 -t latest # Result in two tags: v1.0.0, latest
+```
+
 ## 3. Update Executor in JinaHub
 
 ### 3.1 Basic
@@ -115,15 +123,19 @@ $ jina hub push [--public/--private] --force <UUID> --secret <SECRET> -t TAG <pa
 ### 4.1 Docker Image
 
 ```bash
-$ jina hub pull jinahub+docker://<UUID>[:<SECRET>]
+$ jina hub pull jinahub+docker://<UUID>[:<SECRET>][/<TAG>]
 ```
 
-You can find the Executor by running this command `docker images`.
+You can find the Executor by running this command `docker images`. You can also indicate which version of the Executor you want to use by naming the `/<TAG>`.
+
+```bash
+$ jina hub pull jinahub+docker://DummyExecutor/v1.0.0
+```
 
 ### 4.2 Source Code
 
 ```bash
-$ jina hub pull jinahub://<UUID>[:<SECRET>]
+$ jina hub pull jinahub://<UUID>[:<SECRET>][/<TAG>]
 ```
 
 It will store Executor source code to `~/.jina/hub-packages`.
@@ -148,6 +160,8 @@ from jina import Flow
 f = Flow().add(uses='jinahub+docker://<UUID>[:<SECRET>][/<TAG>]')
 ```
 
+If there is no `/<TAG>` provided when using, it by default equals to `/latest`, which means using the `latest` tag.
+
 **Attention:**
 
 If you are a Mac user, please use `host.docker.internal` as your url when you want to connect a local port from Executor
@@ -185,7 +199,7 @@ any of these parameters by passing `uses_with` and `uses_metas` as parameters.
 ```python
 from jina import Flow
 
-f = Flow().add(uses='jinahub://<UUID>[:<SECRET>]', 
+f = Flow().add(uses='jinahub://<UUID>[:<SECRET>][/<TAG>]', 
                uses_with={'param1': 'new_value'},
                uses_metas={'name': 'new_name'})
 ```