docs: Add integrations / ecosystem section

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Description

I propose to add an integration/ecosystem section to our user guide. The goal would be to show users that Polars is becoming a mature tool that works well with other libraries/tools they use on a daily basis. Initially it should be a simple overview with a couple of categories and a link to either a tutorial or the website.

We can also improve the section by adding specific code examples. I know that @braaannigan currently works on a page about visualisation. It could look something like this:

• Ecosystem(.md) > page with general overview divided into categories
  • visualisations(.md) > page with specific examples around data visualisation
  • ML(.md) > page with examples about polars + scikit learn and other tools
  • other..

Another option I can think of is to merge the visualisation examples into the ecosystem page. Then we have all the examples and libraries in one place.

What do you think? @c-peters @braaannigan

Link

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