Create custom-step-templates folder, move docs/projects/custom-step-templates.md -> docs/projects/custom-step-templates/index.mdx, add custom-step-templates/custom-step-templates-stored-in-git.md

Create custom-step-templates folder, move docs/projects/custom-step-templates.md -> docs/projects/custom-step-templates/index.mdx, add custom-step-templates/custom-step-templates-stored-in-git.md #2019