Documentation: Update coding style rules about comments

The requirement to use // for comments wasn't described anywhere, so now
it is! Also updated the rule about TODO comments because we've allowed
those for a while now.

Documentation/CodingStyle.md

@@ -496,24 +496,31 @@ UniqueObject& my_unique_object(); // Free function.
 
 ### Comments
 
-Make comments look like sentences by starting with a capital letter and ending with a period (punctuation). One exception may be end of line comments like this `if (x == y) // false for NaN`.
+Comments should be written using `//` and not `/* */`, except for the copyright notice.
+
+Make comments look like sentences by starting with a capital letter and ending with a period (punctuation). One exception may be end of line comments like this: `if (x == y) // false for NaN`
+
+While we have no fixed rule about line length, please wrap long comments onto multiple lines so that they are easier to read.
 
 Use FIXME: (without attribution) to denote items that need to be addressed in the future.
+TODO: (without attribution) is also permitted.
 
 ###### Right:
 
 ```cpp
 draw_jpg(); // FIXME: Make this code handle jpg in addition to the png support.
 ```
 
-###### Wrong:
+###### OK:
 
 ```cpp
-draw_jpg(); // FIXME(joe): Make this code handle jpg in addition to the png support.
+draw_jpg(); // TODO: Make this code handle jpg in addition to the png support.
 ```
 
+###### Wrong:
+
 ```cpp
-draw_jpg(); // TODO: Make this code handle jpg in addition to the png support.
+draw_jpg(); // FIXME(joe): Make this code handle jpg in addition to the png support.
 ```
 
 Explain *why* the code does something. The code itself should already say what is happening.