Use a better example in the README

README.md

@@ -13,14 +13,16 @@ Tagref works with any programming language, and it respects your `.gitignore` fi
 Tagref allows you to annotate your code with *tags* (in comments) which can be *referenced* from other parts of the codebase. For example, you might have a tag like this:
 
 ```python
-# [tag:cities_nonempty] There should be at least one city here.
-cities = ['San Francisco', 'Tokyo']
+# [tag:polynomial_nonzero] This function never returns zero.
+def polynomial(x):
+  return x ** 2 + 1
 ```
 
-Elsewhere, suppose you're writing some code which depends on that fact. You can make that clear by referencing the tag:
+Elsewhere (possibly in a different file), suppose you're writing some code which depends on that fact. You can make that clear by referencing the tag:
 
 ```python
-first_city = cities[0] # This is safe due to [ref:cities_nonempty].
+def inverse_polynomial(x):
+  return 1 / polynomial(x) # This is safe due to [ref:polynomial_nonzero].
 ```
 
 To help you manage these tags and references, Tagref checks the following: