message: Add difference from Google C++ style guide: 100 character line limit.
diff: @@ -26,6 +26,7 @@ We welcome contributions from the community. Here are some guidelines.
  * Struct/Class member variables have a '\_' postfix (e.g., "int foo\_;").
  * There are probably a few other things missing from this list. We will add them as they
  are brought to our attention.
  +* 100 columns is the line limit.
  # Submitting a PR
  