markdown: a paragraph an editor wrapped reads as running text

`breaks` is on because the diary is written a line at a time and a line typed
in the browser is meant. Markdown written elsewhere is usually wrapped at a
width instead — an import, a save over the SFTP mount from vim with
`textwidth`, a pasted README — and kept its breaks, one in the middle of every
sentence, worst on a phone.

`hardWrapped` tells the two apart by what a wrapping editor leaves behind:
every line but the last is long, each break comes where the next word would
not have fitted on the line before, and the lines seldom end where a sentence
does. A paragraph that looks like that has its soft breaks read as spaces; a
break asked for outright, two spaces or a backslash at the end of the line,
stays. Lines broken by hand — a short sentence and then another, a list of
things that happened, a verse — keep their breaks as before.

docs/wiki/Writing.md

@@ -46,7 +46,11 @@ Each save keeps the text it replaces, so nothing written is lost. See
 ## Markdown
 
 Documents are GitHub-flavoured markdown: headings, lists, task lists, tables,
-quotes, code blocks and links. A single line break is kept as a line break.
+quotes, code blocks and links. A single line break is kept as a line break,
+the way it was typed, with one exception: a paragraph that an editor wrapped
+at a fixed width, as imported notes and files saved over the SFTP mount often
+are, is read as the running text it is. A break asked for outright, with two
+spaces or a `\` at the end of the line, is always kept.
 
 Math is set by KaTeX: