README: four sentences fixed for the documents gate (closes #229)

The documents gate on `next` failed five README sentences
(#219 (comment)). Four
are rewritten after a check against the code: the keywords score
sentence is split in two; `mlData` drops the whole `clip` block, as
`src/backup.ts` and `src/metadata-backup.ts` do; a file name gets its
ID past 255 bytes and a collection name past 250, and either is then
cut short, as `uniqueNames` does; `lastTriedAt` is taken once per run,
after its refresh. The IDs sentence keeps `-1`: the pinned option
parser passes a negative number to a command with no subcommands as an
argument, so `quak get -1` reaches the ID check. Nothing else changes;
`make fmt` reflowed the touched paragraphs.

Model: fable-5-1

README.md

@@ -1079,10 +1079,10 @@ cached, so the next fetch asks for it again. The reasons are kept in memory
 only.
 
 `lib.close()` stops the background timer. It can be called more than once. A
-refresh in flight is left to finish, with its write to the cache. `close()`
+refresh in flight is left to finish, with its write to the cache. The promise
-returns a promise. It resolves once that refresh, the machine-learning fetch and
+`close()` returns resolves once that refresh, the machine-learning fetch and the
-the background downloads already running have all finished. The cache directory
+background downloads already running have all finished. The cache directory can
-can then be removed. After `close()`, `fresh()`, `freshCollections()`,
+then be removed. After `close()`, `fresh()`, `freshCollections()`,
 `freshFiles()` and `lib.backup()` reject with `the library is closed`.
 
 ### Default reads and fresh reads