Add note about long format strings

Author: Techassi

modules/contributor/pages/code-style-guide.adoc

@@ -314,7 +314,12 @@ enum Error {
 === Named versus unnamed format string identifiers
 
 For simple string formatting (up to two substitutions), we allow unnamed (and thus also uncaptured) identifiers.
+
 For more complex formatting (more than two substitutions), we require named identifiers to avoid ambiguity, and to decouple argument order from the text (which can lead to incorrect text when the wording is changed and `{}` are reordered while the arguments aren't).
+This rule needs to strike a balance between explicitness and concise `format!()` invocations.
+Long `format!()` expressions can lead to rustfmt breakage.
+It might be better to split up long formatting strings into multiple smaller ones.
+
 Mix-and-matching of named versus unnamed identifiers must be avoided.
 See the next section about captured versus uncaptured identifiers.