[to admin] Change a docs page on Matrix Vector about derivatives

Rashid Umarov #:

Will be improved as soon as possible. For a while you can use this include file as a reference.

Thank you .

Meanwhile you could change the documentation page and inform coders about it .

If you change anything in the future then you will change the documentation page again . 

It's not that time consuming and it will save a lot of time .

Imagine if someone is starting out , they have all the math to digest and they will have this blindside them too.

(also can this mqh be used in codebase publications ?)