inject environment variable

 is added to the environment for all CLI requests VIT makes

vit/process.py

@@ -14,6 +14,7 @@ def __init__(self, config):
         self.config = config
         self.env = env.user.copy()
         self.env['TASKRC'] = self.config.taskrc_path
+        self.env['IS_VIT_COMMAND'] = "1"
 
     def run(self, command, capture_output=False, custom_env={}):
         if isinstance(command, str):