Refactoring README for better readability

[saccarosium]

Hi, This PR makes the following changes:

• Fix typos and Casing issues
• Center images
• Use hyperlinks to headings for better navigation
• Clear redundant examples
• Rethink the structure of the readme for better organisation.

Also I would like to know your thoughts on what documentation you will confident maintaining. At the moment we are using both README and vimdoc internal documentation, that seems to be very outdated and not useful. As I see it we can go with 3 different approaches:

1. Remove the vimdoc and maintain only the README;
2. Remove the documentation from the README and maintain only the vimdoc;
3. We maintain only the README and out generate the vimdoc, manually or automatically with pandoc.

[CRAG666]

I choose option 3