README.md rewritten sentence by sentence (closes #219)

The old text served as the list of what to cover. The new text leads
with what quak is, what it is for and how to use it. Every command,
option, exit code and file layout follows in reference sections, then the
library reference, then design, entrypoints and development. Every
statement was checked against the code on next; the pull request lists
each disagreement. Sentences stay under about 30 words, tables are lists,
and no issue links or project history remain in text for users. Two code
comments now name the new README sections, and the one in
`src/cli-log.ts` matches "What quak prints" on stderr, stdout and exit
status; a third no longer cites the README.

Model: fable-5-1

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);