doc: fast-import: replace literal block with paragraph

68061e3 (fast-import: disallow "feature export-marks" by default,
2019-08-29) added the documentation for this option.  The second
paragraph is a literal block but it looks like it should just be
a regular paragraph.

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: LemmingAvalanche

Documentation/git-fast-import.adoc

@@ -61,10 +61,10 @@ OPTIONS
 	currently impacts only the `export-marks`, `import-marks`, and
 	`import-marks-if-exists` feature commands.
 +
-	Only enable this option if you trust the program generating the
-	fast-import stream! This option is enabled automatically for
-	remote-helpers that use the `import` capability, as they are
-	already trusted to run their own code.
+Only enable this option if you trust the program generating the
+fast-import stream! This option is enabled automatically for
+remote-helpers that use the `import` capability, as they are
+already trusted to run their own code.
 
 Options for Frontends
 ~~~~~~~~~~~~~~~~~~~~~