docs: add note on spark env

Author: kenjis

user_guide_src/source/general/environments.rst

@@ -24,6 +24,10 @@ the value provided in ``$_SERVER['CI_ENVIRONMENT']``, otherwise defaulting to
     It has special conditions built into the framework at various places to assist with that.
     You can't use it for your development.
 
+.. note:: You can check the current environment by ``spark env`` command::
+
+    > php spark env
+
 .env
 ----
 
@@ -33,6 +37,10 @@ The simplest method to set the variable is in your :doc:`.env file </general/con
 
     CI_ENVIRONMENT = development
 
+.. note:: You can change the ``CI_ENVIRONMENT`` value in **.env** file by ``spark env`` command::
+
+    > php spark env production
+
 Apache
 ------