Add suggestions for Leap on Javascript

tracks/javascript/exercises/leap/README.md

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+### Reasonable solutions
+
+```javascript
+module.exports = {
+  isLeap(year) {
+        if (this.year % 4 !== 0) return false
+
+        if (this.year % 100 !== 0) return true
+
+        if (this.year % 100 === 0 && this.year % 400 === 0) return true
+
+        return false
+  }
+}
+```
+
+### Common suggestions
+
+- For solutions that have more than one exit point, suggest trying to use a single
+exit point while maintaining legibility. It could be done by aggregating all
+conditionals in one and creating a temp var with a legible name for each.
+
+- Creating a helper function that checks if a number is divisible might also be
+a good idea. This would help with the first point and keep the logic readable.
+[Here is a good example of it](https://exercism.io/tracks/javascript/exercises/leap/solutions/caa4742c2be14884848044f9bcfbb775)
+
+### Talking points
+
+- Although this exercise is quite simple it is worth talking about the dangers of
+having functions with a lot of branching and specially when they lead to exit points.
+
+- If there is a boolean check that returns `true` or `false` then just returning the
+result of the boolean operation might achieve the same result.