cmdline-docs: quote and angle bracket cleanup

- make sure angle brackets are escaped
- remove a lot of superfluous double quotes
- replace several double quotes with backticks

To make nicer-looking markdown.

Closes #12884

docs/cmdline-opts/MANPAGE.md

@@ -83,6 +83,9 @@ explicitly with an empty "header":
 
     ##
 
+Angle brackets (`<>`) need to be escaped when used in text like `\<` and
+`\>`. This, to ensure that the text renders nicely as markdown.
+
 ### Headers
 
 The `#` header can be used by non-option files and it produces produces a