docs: explain setups without a ZIP

FAQ entry, the release_pack field and how to revisit it from download
counts, the get/ pages, and RetroPie 4.8 now installs from a computer with
the Pi's network folder as --dest. The start pages are back under their
word ceilings.

wiki/adding-a-platform.md

@@ -160,6 +160,7 @@ platforms:
   myplatform:
     config: myplatform.yml           # platform YAML filename in platforms/
     status: active                   # active or archived
+    release_pack: true               # optional: a release publishes its ZIP
     device_group: handheld           # computer, gaming-os, handheld, fpga or server
     scraper: myplatform              # matches PLATFORM_NAME, null if hand-maintained
     schedule: weekly                 # re-scrape cadence, run by hand: weekly, monthly, or null
@@ -682,6 +683,12 @@ A new platform is archived-by-default nowhere: `status: active` puts it in
 `status: archived` to keep the configuration without the automation. Archived
 platforms are excluded unless `--all` or `--include-archived` is passed.
 
+A new platform has no release ZIP: `release_pack: true` is set for the setups
+most people download, and the installer serves every other one from its
+manifest. `generate_pack.py --platform myplatform` still builds its pack.
+[Which platforms get a pack](release-process.md#which-platforms-get-a-pack)
+says how the list is read from download counts.
+
 Check the output for:
 
 - The new platform appears in verify results