* Updated index.md
I have provided more info about what the solution that cards grant you and what key features can be created using cards
* Grammar fixes
changed sentence "you need to create a ```<div>``` container with the class ```.card``` and inside another ```<div>``` container" to "you need to create a ```<div>``` container with the class ```.card``` and inside of that another ```<div>``` container"
* Fixed markdown and examples
* Fixed markdown in starting section and 'Header and Footer' section
* Fixed example code structure in starting section and 'Header and Footer' section
* Add correct syntax
RonnyNovik
Bro3Simon
Tom K
Kamil
trbst
Mrugesh Mohapatra