Update the HRMP channel guide

[gluneau]

Is there an existing issue?

• [X] I have searched the existing issues

Experiencing problems? Have you tried our Stack Exchange first?

• [X] This is not a support question.

Content request

The existing guide needs an update and a proper place in the nav.

https://docs.substrate.io/reference/how-to-guides/parachains/add-hrmp-channels/

Please inform me when done and I will link to it from Acala's wiki guide to onboard parachains.

Are you willing to help with this request?

Yes!

[nuke-web3]

@gluneau can you link to where you intend to use this content and give some context about what you need it for there?

Overall I hope this spurs more collaboration and requests for content that you feel should live on the docs here for your needs and the parachain teams at large in their docs!

[lisa-parity]

@gluneau, can you take a look at https://docs.substrate.io/tutorials/connect-relay-and-parachains/open-message-passing-channels/ and see if that works for you?