docs(argo-workflows): Add MySQL persistence support explicitly on README (#2448)

charts/argo-workflows/values.yaml

@@ -146,7 +146,8 @@ controller:
     capabilities:
       drop:
         - ALL
-  # -- enable persistence using postgres
+  # -- enable Workflow Archive to store the status of workflows. Postgres and MySQL (>= 5.7.8) are available.
+  ## Ref: https://argo-workflows.readthedocs.io/en/latest/workflow-archive/
   persistence: {}
   # connectionPool:
   #   maxIdleConns: 100
@@ -171,6 +172,17 @@ controller:
   #   # sslMode must be one of: disable, require, verify-ca, verify-full
   #   # you can find more information about those ssl options here: https://godoc.org/github.com/lib/pq
   #   sslMode: require
+  # mysql:
+  #   host: localhost
+  #   port: 3306
+  #   database: argo
+  #   tableName: argo_workflows
+  #   userNameSecret:
+  #     name: argo-mysql-config
+  #     key: username
+  #   passwordSecret:
+  #     name: argo-mysql-config
+  #     key: password
 
   # -- Default values that will apply to all Workflows from this controller, unless overridden on the Workflow-level.
   # Only valid for 2.7+