added JiffyLoad.com

I'm not a native speaker but the description feels really jumpy to me.

`in real browser` -> `in real browsers`

`Yslow` -> `YSlow`

`Service captures video and screenshot of loading and provides tips to improve website performance.` -> `The service captures video and screenshots of loaded pages and provides tips to improve overall performance.`

Please tell me if you agree. :bowtie: