docs: name the part marker in the release steps

wiki/release-process.md

@@ -213,7 +213,9 @@ python scripts/pipeline.py --include-archived
 # 2. A release file must be under 2 GiB. A larger pack becomes parts that are
 #    each a ZIP of whole files (Pack.part1of2.zip): any tool opens one, and
 #    the parts extracted into one folder are the pack. Each part is read back
-#    and the set compared with the pack before the pack is removed.
+#    and the set compared with the pack before the pack is removed. Each part
+#    also holds a marker (Pack.part1of2.txt) naming every part and its size,
+#    which install.py --check reads to name a part missing from a folder.
 python scripts/split_pack.py dist/
 
 # 2b. The handheld port, RetroBIOS.zip, built from ports/RetroBIOS with the

wiki/tools.md

@@ -688,7 +688,7 @@ python scripts/refresh_stale.py --only platforms,targets --jobs 6
 | `list_platforms.py` | List active platforms (`--include-archived` adds the archived ones, used by CI) |
 | `download.py` | Download a pack from GitHub releases, every part checked (Python, stdlib only) |
 | `download.sh` | Same, as a shell one-liner (`curl` + `unzip`) |
-| `split_pack.py` | Cut a pack over the release asset limit into parts that are each a ZIP of whole files, read back before the pack is removed |
+| `split_pack.py` | Cut a pack over the release asset limit into parts that are each a ZIP of whole files, each with a marker naming every part, read back before the pack is removed |
 | `provenance_report.py` | Dump-catalog coverage and acquisition targets (see above) |
 | `find_pinned_revision.py` | Walk the upstream commits that touched a file and return the revision whose bytes match a platform's pinned md5 (`--write` saves them) |
 | `generate_readme.py` | Generate README.md and CONTRIBUTING.md from database |