docs: fix typo in alternator/getting-started.md
docs: fix typo in alternator/getting-started.md

alternator/getting-started.md had a missing grave accent (`) character,
resulting in messed up rendering of the involved paragraph. Add the missing
quote.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>
Message-Id: <20200827110920.187328-1-625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,avikivity/scylla