Add Edition Differences to conventions section
@@ -79,6 +79,12 @@ information. These conventions are documented here.
An *example term* is an example of a term beind defined.
+* Differences in the language by which edition the crate is compiled under are
+ in a blockquote that start with the words "Edition Differences:" in **bold**.
+
+ > **Edition Differences**: In the 2015 edition, this syntax is valid that is
+ > disallowed as of the 2018 edition.
+
* Notes that contain useful information about the state of the book or point out
useful, but mostly out of scope, information are in blockquotes that start
with the word "Note:" in **bold**.
