Update external-datastore.md (#646)

* Update external-datastore.md

* fix linter

docs/src/snap/howto/external-datastore.md

@@ -27,7 +27,7 @@ Create a configuration file and insert the contents below while replacing
 the placeholder values based on the configuration of your etcd cluster.
 
 ```yaml
-datastore: external
+datastore-type: external
 datastore-url: "<etcd-member-addresses>"
 datastore-ca-crt: |
   <etcd-root-ca-certificate>
@@ -36,9 +36,10 @@ datastore-client-crt: |
 datastore-client-key: |
   <etcd-client-key>
 ```
-
+<!-- markdownlint-disable -->
 * `datastore-url` expects a comma seperated list of addresses
   (e.g. `https://10.42.254.192:2379,https://10.42.254.193:2379,https://10.42.254.194:2379`)
+<!-- markdownlint-restore -->
 * `datastore-ca-crt` expects a certificate for the CA in PEM format
 * `datastore-client-crt` expects a certificate that's signed by the root CA
   for the client in PEM format