Have a way to add comment

[r0b0ji]

Currently, there is a fixed comment _comment = "#dotbot-crontab" added to each cron. It'd be better if user can provide comment describing their cron job. It can be done by an optional field apart from mandatory cron and command. The data can have a field say comment and if present use the comment from entry, else use the default.

[r0b0ji]

It can be done as simple as by changing the line

--- row = "{} {} {}".format(entry["cron"], entry["command"], self._comment)
+++ row = "{} {} {}".format(entry["cron"], entry["command"], entry.get("comment", self._comment))