Use the given merge strategy; can be supplied more than
once to specify them in the order they should be tried.
If there is no `-s` option, a built-in list of strategies
- is used instead (`git-merge-recursive` when merging a single
- head, `git-merge-octopus` otherwise).
+ is used instead ('git-merge-recursive' when merging a single
+ head, 'git-merge-octopus' otherwise).