Update boolean_variables.rst
Adding explanation on what is considered valid input for boolean configuration.
@@ -20,7 +20,10 @@ you'd get the following user input when running Cookiecutter::
run_as_docker [True]:
-Depending on the user's input, a different condition will be selected.
+The following values are considered valid input:
+
+ true, 1, yes, y **or**
+ false, 0, no, n
The above ``run_as_docker`` boolean variable creates ``cookiecutter.run_as_docker``, which
can be used like this::
