Fix navbar design

Before had a margin left in link_menu.

Then it was removed while window width to be equal or less than 600px.

Before, the navbar had one more item, but this item was removed

Now, this is result.

Fix wrong links in README

Nothing special in this version, just fixed wrong link.

Limits Gym: first product version

This is the first realese. New updates will be released in the future, bringing a product purchase system.