docs: add Akash SDL community contribution guide (#1201)

Adds a beginner-oriented walkthrough of the Akash SDL format to the
Community Contributions collection, contributed by Rodri.

Successor to #1097, which bundled this guide together with an unrelated
OpenClaw guide that had missing image references and was blocking CI.
This PR ships only the SDL guide, which is build-clean on its own.

Signed-off-by: Sam Lister <listersb@gmail.com>
Co-authored-by: Rodri <rochas.dev@hotmail.com>
Co-authored-by: Zeke <105066639+Zblocker64@users.noreply.github.com>
Co-authored-by: panther <hoomandigital377@gmail.com>

Author: 4 people