docs: Add Markdown inline code marker around inline XML example.

Presently, this tag is not rendered --- by Gitiles, at least --- which
makes the example very confusing indeed.

Signed-off-by: Jashank Jeremy <jashank@rulingia.com.au>
Change-Id: Ia76a60d8ee0ecce8ceb32661afbd48f3b2d80fbf
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/291362
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Jashank Jeremy <jashank.jeremy@gmail.com>

docs/manifest-format.md

@@ -267,7 +267,7 @@ Attribute `groups`: List of groups to which this project belongs,
 whitespace or comma separated.  All projects belong to the group
 "all", and each project automatically belongs to a group of
 its name:`name` and path:`path`.  E.g. for
-<project name="monkeys" path="barrel-of"/>, that project
+`<project name="monkeys" path="barrel-of"/>`, that project
 definition is implicitly in the following manifest groups:
 default, name:monkeys, and path:barrel-of.  If you place a project in the
 group "notdefault", it will not be automatically downloaded by repo.