update readme

Author: cemkiy

README.md

@@ -23,7 +23,7 @@ $ pip3 install real_environment
 from real_environment import real_environment
 # init func will autoload your .env file
 renv = real_environment.RealEnvironment()
-renv.get_env_or_default("db_url","")
+renv.get_env_or_default("db_url","default_value_if_empty_returns")
 renv.set_a_variable_to_environment("key","value")
 renv.remove_a_variable_from_environment("key")
 ```