Docs: add note for arrow functions in no-seq rule (#14578)

docs/rules/no-sequences.md

@@ -39,8 +39,6 @@ switch (val = foo(), val) {}
 while (val = foo(), val < 42);
 
 with (doSomething(), val) {}
-
-const foo = (val) => (console.log('bar'), val);
 ```
 
 Examples of **correct** code for this rule:
@@ -63,8 +61,32 @@ switch ((val = foo(), val)) {}
 while ((val = foo(), val < 42));
 
 with ((doSomething(), val)) {}
+```
+
+### Note about arrow function bodies
+
+If an arrow function body is a statement rather than a block, and that statement contains a sequence, you need to use double parentheses around the statement to indicate that the sequence is intentional.
+
+Examples of **incorrect** code for arrow functions:
+
+```js
+/*eslint no-sequences: "error"*/
+const foo = (val) => (console.log('bar'), val);
+
+const foo = () => ((bar = 123), 10));
+
+const foo = () => { return (bar = 123), 10 }
+```
+
+Examples of **correct** code for arrow functions:
 
+```js
+/*eslint no-sequences: "error"*/
 const foo = (val) => ((console.log('bar'), val));
+
+const foo = () => (((bar = 123), 10));
+
+const foo = () => { return ((bar = 123), 10) }
 ```
 
 ## Options