doc/_ext: claim ceph_releses ext to be parallel read safe

so we can pass `-j auto` to sphinx-build to speed up the build

Signed-off-by: Kefu Chai <kchai@redhat.com>

doc/_ext/ceph_releases.py

@@ -210,3 +210,7 @@ class CephTimeline(Directive):
 def setup(app):
     app.add_directive('ceph_releases', CephReleases)
     app.add_directive('ceph_timeline', CephTimeline)
+    return {
+        'parallel_read_safe': True,
+        'parallel_write_safe': True
+    }