Apply suggestions from code review #282

Review by @blackwinter

Author: TobiasNx

README.md

@@ -269,16 +269,15 @@ put_vars(
 
 ##### `to_var`
 
-Defines a single global variable that can be referenced with `$[<variableName>]` and assinges the value of the `<sourceField>`.
+Defines a single global variable that can be referenced with `$[<variableName>]` and assigns the value of the `<sourceField>`.
 
 ```perl
-to_var("<sourceField>", "<variableValue>")
+to_var("<sourceField>", "<variableName>")
 ```
 
 Options:
 
-- `"default"`: provide default value if source field does not exist.
-
+- `default`: Default value if source field does not exist. The option needs to be written in quotation marks because it is a reserved word in Java. (Default: Empty string)
 
 [Example in Playground](https://metafacture.org/playground/?example=to_var)