doc: move enum methods to enum section from sum types (#13843)

doc/docs.md

@@ -3095,6 +3095,50 @@ Output: `Grocery IDs: 0, 5, 6`.
 
 Operations are not allowed on enum variables; they must be explicitly cast to `int`.
 
+Enums can have methods, just like structs.
+
+```v
+enum Cycle {
+	one
+	two
+	three
+}
+
+fn (c Cycle) next() Cycle {
+	match c {
+		.one {
+			return .two
+		}
+		.two {
+			return .three
+		}
+		.three {
+			return .one
+		}
+	}
+}
+
+mut c := Cycle.one
+for _ in 0 .. 10 {
+	println(c)
+	c = c.next()
+}
+```
+
+Output:
+```
+one
+two
+three
+one
+two
+three
+one
+two
+three
+one
+```
+
 ### Sum types
 
 A sum type instance can hold a value of several different types. Use the `type`
@@ -3145,50 +3189,6 @@ fn main() {
 }
 ```
 
-Enums can have methods, just like structs
-
-```v
-enum Cycle {
-	one
-	two
-	three
-}
-
-fn (c Cycle) next() Cycle {
-	match c {
-		.one {
-			return .two
-		}
-		.two {
-			return .three
-		}
-		.three {
-			return .one
-		}
-	}
-}
-
-mut c := Cycle.one
-for _ in 0 .. 10 {
-	println(c)
-	c = c.next()
-}
-```
-
-Output:
-```
-one
-two
-three
-one
-two
-three
-one
-two
-three
-one
-```
-
 #### Dynamic casts
 
 To check whether a sum type instance holds a certain type, use `sum is Type`.