Add missing "prints" comment.

The old tested version used << for a silent expectation, so it might
have been intentional that we omitted this.  However, the commit [1]
that added this example doesn't call out any reason for omitting the
"prints" comment, so I'm guessing it was an oversight.  Either way, it's
better to be consistent -- this was the only call to print(...) that
didn't have a comment.

[1] dda4562

Author: amartini51

Sources/TSPL/TSPL.docc/GuidedTour/GuidedTour.md

@@ -270,6 +270,7 @@ Arrays automatically grow as you add elements.
 ```swift
 fruits.append("blueberries")
 print(fruits)
+// Prints "["strawberries", "grapes", "tangerines", "blueberries"]"
 ```
 
 <!--
@@ -278,7 +279,7 @@ print(fruits)
   ```swifttest
   -> fruits.append("blueberries")
   -> print(fruits)
-  << ["strawberries", "grapes", "tangerines", "blueberries"]
+  <- ["strawberries", "grapes", "tangerines", "blueberries"]
   ```
 -->