Add a rule about the indentation of multi-arity functions

Author: wjlroe

README.md

@@ -137,9 +137,9 @@ You can generate a PDF or an HTML copy of this guide using
  (defn foo
   ([x] (bar x))
   ([x y]
-   (if (predicate? x)
-   (bar x)
-   (baz x))))
+  (if (predicate? x)
+  (bar x)
+  (baz x))))
 
  ;; bad
  (defn foo
@@ -148,6 +148,28 @@ You can generate a PDF or an HTML copy of this guide using
   (baz x)))
  ```
 
+* <a name="multiple-arity-indentation"></a>
+ Indent each arity form of a function definition vertically aligned with its
+ parameters.<sup>[[link](#multiple-arity-indentation)]</sup>
+
+```Clojure
+;; good
+(defn foo
+ "I have two arities."
+ ([x]
+ (foo x 1))
+ ([x y]
+ (+ x y)))
+
+;; bad - extra indentation
+(defn foo
+ "I have two arities."
+ ([x]
+ (foo x 1))
+ ([x y]
+ (+ x y)))
+```
+
 * <a name="align-docstring-lines"></a>
  Indent each line of multi-line docstrings.
 <sup>[[link](#align-docstring-lines)]</sup>