convert: use field list instead of option list in help
Use field list instead of option list in convert help, because the
option list format used, with defaults and type of argument is not
supported by docutils.
$ hg init a
$ echo a > a/a
$ hg -R a ci -A -m a
adding a
$ hg clone a b
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo b > b/b
$ hg -R b ci -A -m b
adding b
$ chmod 100 a/.hg/store
$ hg -R b push a
pushing to a
abort: could not lock repository a: Permission denied
[255]
$ chmod 700 a/.hg/store