Add a ## Docs section to highlight the docs URL

[VinGarcia]

References to other Issues or PRs

As suggested on issue #1882
I am creating this PR to make the link to the documentation site
more visible on the README file.

Brief description of what is fixed or changed

Add a ### Docs section to the README file.

Other comments

It was also suggested that I created a ### Customizing your gateway section to the README, but I don't feel qualified yet for writing this section, so I just created this first one.

It is also worth noting that the docs already have a Customizing your gateway section which will be very helpful if more people find this page.

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[johanbrandhorst]

LGTM

[johanbrandhorst]

Could you please sign the CLA and reply to the bot?

[VinGarcia]

@googlebot I signed it!

[VinGarcia]

Done @johanbrandhorst, is there anything else?

[johanbrandhorst]

Nah, that was it! The fuzzit job has started failing occasionally, unfortunately. I reran it once, but it was still unhappy so we'll just leave it. Thanks for your contribution 😄.