Creation of ReadMe Doc to completely explain how to modify portfolio.js

[ashutosh1919]

In our current doc, we just mentioned that user needs to modify portfolio.js but we didn't explain each of the components seperately.

It is good that we create seperate readme file named CUSTOMISE_PORTFOLIO.md and add every instruction to customize every block in portfolio.js

[ashutosh1919]

@danielmarostica , since you have successfully customised website and you may have idea about what problem you faced while customising. So, do you want to work on it?

[danielmarostica]

Of course!