Add Banner to README file

[cesaralvrz]

I added the banner to the README file with a title with align to the center.

Also fixed a broken error for the website of Python Canarias.

[jdevera]

First of all, thank you for this first contribution! 🎉 🎉 🎉

Also, really nice banner! 😍

I left a comment about the image URL, and here are some more that I could not attach to the right file because github will not let me comment on whole files:

• Please rename the PyCa.png to something more descriptive, such as python_canarias_banner.png (I changed the casing here just for personal preference, it's not important as long as it does not have spaces in the name)
• Please move the assets folder to be under the docs folder, this makes it extra clear it's not part of the app. Note this will require changing the path in the README too.

One meta topic: This PR comes from a conversation somewhere else and I have that context, so it's fine, but generally it is best to also include the motivation of the PR in the description itself. Not only for the reviewers of now but also for future reference.

And one topic for discussion: I noticed the banner image is larger than it ever renders in Github. Github caps this as 838px in width no matter how much bigger I make the viewport.

I think we should optimise this in a repository that is otherwise used for coding an app. If your original work on the banner comes from a vector graphics file such as SVG, It'd be great to also contribute that to the docs repository, while the image we store in this repo is the one optimised for its current use: show up in the README. What do you think?

[jdevera]

The banner image URL points to your own fork. Once this PR is merged, it would continue to point to your fork. For images that are also hosted in the repositories, the preference is to use relative paths to them. In this case, this would look like this:

Suggested change

	
	

[cesaralvrz]

The original work is also in PNG, but if you want I can add the banner in the original size to the docs repository.

[jdevera]

Thank you for the additional changes! Looks great!

[sdelquin]

Gracias @cesaralvrz por la colaboración altruista y gracias @jdevera por revisarlo y mergearlo 😄