README: the close() sentence split in two (closes #231)

The sentence in "Opening a library" had a relative clause with its
"that" left out, so "returns resolves" read as two verbs in a row. It
is now two sentences; the behaviour described is unchanged and matches
`close()` in `src/library/index.ts`.

Model: fable-5-1 (change); opus-5-5 (landing message)

src/cli-log.ts

@@ -1,15 +1,18 @@
 // The CLI's log level, and the one function the commands write stderr lines
 // through.
 //
-// Every line quak prints on stderr is a log line at one of six levels, from
+// Every line quak logs goes to stderr, at one of six levels, from the
-// the quietest: fatal, error, warning, info, debug, trace. A run prints the
+// quietest: fatal, error, warning, info, debug, trace. A run prints the lines
-// lines at its own level and at every quieter one. Its level is info unless
+// at its own level and at every quieter one. Its level is info unless `-v` or
-// `-v` or `-q` asks for another (see "CLI surface" in the README). Every
+// `-q` asks for another (see "What quak prints" in the README). A command that
-// command that exits non-zero logs a fatal line saying why, so even `-q`, which
+// runs and exits non-zero logs a fatal line saying why, so even `-q`, which
-// prints only fatal lines, never leaves a non-zero exit unexplained. An error
+// prints only fatal lines, never leaves such an exit unexplained. An error
 // line reports something that failed, such as a file or an album, and a
 // warning something that did not fail but needs the user's attention. stdout
-// carries only a command's output and is not a log.
+// carries a command's output and the prompts of `login`, and is not a log.
+// Two things on stderr are not log lines: the `error:` message for a
+// command line that quak cannot parse, and the usage printed when no command
+// is given.
 //
 // The library itself writes no lines: its layers report through callbacks, and
 // the CLI logs what they report. `logRequests` gives the API client options

test/cli/backup-end-to-end.test.ts

@@ -418,7 +418,7 @@ describe("the first backup of the account", () => {
         expect(downloads.sort()).toEqual([100, 200, 300]);
     });
 
-    // The tree "Backup layout" in the README describes. Each original is at
+    // The tree under "The backup directory" in the README. Each original is at
     // its save path, `YYYY/YYYY-MM/YYYY-MM-DD/YYYY-MM-DD.<fileID>.<ext>`, with
     // the extension of its title; the live photo is its image and its video,
     // each with the extension it had inside the ZIP, and a `.livephoto.json`

test/cli/log.test.ts

@@ -328,7 +328,7 @@ describe("what the library reports", () => {
         ]);
     });
 
-    // Each operation is named in plain words, as the README names it.
+    // Each operation is named in plain words.
     it("logs a refresh's progress at info, and its start and end at debug", () => {
         const { log, lines } = collect();
         const onProgress = logRefresh(log);