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

The documents gate on `next` failed five README sentences
(#219 (comment)). Four
are replaced with the gate's rewrite 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

@@ -472,8 +472,8 @@ fresh reads"). `backup` counts it as failed (see "What quak cannot decrypt").
 
 A collection ID or file ID given to `files`, `get`, `get-thumb` or
 `fix-missing-thumbnails --file` is written in decimal digits and is at
-most 9007199254740991. Anything else, such as `0x10` or `1e3`, is refused before
+most 9007199254740991. Anything else, such as `0x10`, `1e3` or `-1`, is refused
-any request is sent. The command logs `Invalid file ID: <arg>` or
+before any request is sent. The command logs `Invalid file ID: <arg>` or
 `Invalid collection ID: <arg>` and exits 1.
 
 ### What quak prints
@@ -777,9 +777,10 @@ ignoring case, get their IDs added before the extension: `IMG_0001 (12345).JPG`
 and `IMG_0001 (12346).JPG`. A collection named like another collection's JSON
 file, such as `Trip.json` beside `Trip`, also gets its ID added. A file name
 longer than 255 bytes, the limit on most file systems, gets its ID added too. So
-does a collection name longer than 250 bytes, which leaves room for `.json`. It
+does a collection name longer than 250 bytes, which leaves room for `.json`.
-is then cut short before the ID, just far enough to fit. IDs never change, so a
+Either name is then cut short before the ID, just far enough to fit. IDs never
-name stays the same from run to run until such a clash appears or goes away.
+change, so a name stays the same from run to run until such a clash appears or
+goes away.
 
 Each run removes every symlink in a collection's directory that points into the
 date folders and is not one of its current links, yours included. A file or
@@ -834,8 +835,8 @@ Each entry holds:
 - `fileID` and `title`;
 - `classification`: the kind of failure;
 - `attempts`: how many runs in a row have failed the file;
-- `lastTriedAt`: the start of the run that last tried it, as a Unix time in
+- `lastTriedAt`: when the run that last tried it finished its refresh, as a Unix
-  milliseconds;
+  time in milliseconds;
 - `error`: the error, as quak printed it.
 
 The kinds are: