Update pytorch.org/ignite, README, contributing docs

[vfdev-5]

📚 Documentation

We have now https://pytorch-ignite.ai/ with a lot of helpful resources, examples, tutorials etc.

We need to update the content of

• https://pytorch.org/ignite/ : mention the site and start grqdually removing the header with "Quickstart", "Concepts" etc
• README.md : we should add a link to the site
• CONTRIBUTING.md : should mention Examples repository

cc @Priyansi

[ydcjeff]

Just want to mention that we can use https://pytorch-ignite.ai/chat as a shortcut for discord link.

[sayantan1410]

Hello I would like to contribute to this issue, is it still unassigned ? Can I contribute ?

[Dronten]

can i work on this one