pretty-formats.txt: add missing space

The description of "%ch" is missing a space after "human style", before
the parenthetical remark. This description was introduced in b722d4560e
("pretty: provide human date format", 2021-04-25). That commit also
added "%ah", which does have the space already.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/pretty-formats.txt

@@ -208,7 +208,7 @@ The placeholders are:
 '%ci':: committer date, ISO 8601-like format
 '%cI':: committer date, strict ISO 8601 format
 '%cs':: committer date, short format (`YYYY-MM-DD`)
-'%ch':: committer date, human style(like the `--date=human` option of
+'%ch':: committer date, human style (like the `--date=human` option of
 	linkgit:git-rev-list[1])
 '%d':: ref names, like the --decorate option of linkgit:git-log[1]
 '%D':: ref names without the " (", ")" wrapping.