docs: commit the new-driver checklist, step 2 rewritten for packages

The checklist (with the Intel UHD 750 worked example) existed only as
an untracked file in the main checkout — the plan referenced it but no
branch could see it. It lands here with its build step rewritten
against the finished package template: create the driver's own
build.zig/zon from the pci-bus template, then one dependency + one
boot-tree row + one zon line in the root build. devices-csv.md's
adding-a-driver section and the plan's checklist references point at
it again.

docs/device-driver-development/devices-csv.md

@@ -96,6 +96,9 @@ in different namespaces — against the right `bus` column.
 
 ## Adding a driver
 
+(The step-by-step walkthrough with a worked example is
+[new-driver-checklist.md](new-driver-checklist.md).)
+
 1. Create `system/drivers/<name>/` with the driver source plus a ~15-line
    package `build.zig` + `build.zig.zon` (copy an existing driver package,
    e.g. `system/drivers/pci-bus/`; per-driver extras go through