Merge pull request #1635 from lindboe/clarify-function-definition-vs-execution

Clarify calling functions explanation

Author: das-g

en/python_introduction/README.md

@@ -815,7 +815,7 @@ hi()
 
 Okay, our first function is ready!
 
-You may wonder why we've written the name of the function at the bottom of the file. This is because Python reads the file and executes it from top to bottom. So in order to use our function, we have to re-write it at the bottom.
+You may wonder why we've written the name of the function at the bottom of the file. When we write `def hi():` and the indented lines following, this is us writing instructions for what the `hi()` function should do. Python will read and remember these instructions, but won't run the function yet. To tell Python we want to run the function, we have to call the function with `hi()`. Python reads the file and executes it from top to bottom, so we have to define the function in the file before we call it.
 
 Let's run this now and see what happens: