style guide: Add events and errors to the order of definitions at file level

Author: cameel

docs/style-guide.rst

@@ -1045,13 +1045,15 @@ No:
 Order of Layout
 ***************
 
-Layout contract elements in the following order:
+Contract elements should be laid out in the following order:
 
 1. Pragma statements
 2. Import statements
-3. Interfaces
-4. Libraries
-5. Contracts
+3. Events
+4. Errors
+5. Interfaces
+6. Libraries
+7. Contracts
 
 Inside each contract, library or interface, use the following order: