docs: drop stale references to the cranlike fork

- explain GITHUB_PAT by bincraft's DESCRIPTION reads from the CRAN mirror
- describe how upload_package_index() builds the index in the README

.crow/weekly-rebuild-reindex.yaml

@@ -4,8 +4,8 @@
 # objects in place, so the slot's index still advertises the old MD5 and, for
 # anything that had been served from source, no Built stamp. Re-indexing from
 # inside a shard would mean three concurrent `upload_package_index()` calls on
-# one prefix: `cranlike::update_PACKAGES()` lists the live bucket, so an early
-# lister that uploads last publishes an index missing its siblings' work.
+# one prefix: each lists the live bucket, so an early lister that uploads last
+# publishes an index missing its siblings' work.
 #
 # So it happens exactly once per slot, here, after every shard has finished.
 # `runs_on: [success, failure]` keeps that true when a shard fails; only an
@@ -144,12 +144,11 @@ steps:
         from_secret: PGPASS
       REPO_RO_TOKEN:
         from_secret: REPO_RO_TOKEN
-      # uvr resolves bincraft's dependencies through the GitHub API, including
-      # the pat-s/cranlike@s3 fork. Unauthenticated it is rate limited, and the
-      # failure is not loud: uvr warns, falls back to the registry copy of
-      # cranlike, and the index write then dies on `unused argument (built =
-      # built)` because upstream has no such parameter. Intermittent by nature,
-      # since it depends on the rate-limit window.
+      # bincraft reads the DESCRIPTION of every new or replaced tarball from
+      # the CRAN mirror on raw.githubusercontent.com, and authenticates with
+      # this token when it is set. A slot whose published index cannot be read
+      # is re-read in full, ~25k requests, which the anonymous rate limit would
+      # cut short.
       GITHUB_PAT:
         from_secret: GITHUB_PAT
       GIT_USER: pat-s