update macaroon docs regarding DB types used

[ZZiigguurraatt]

At

lnd/macaroons/README.md

Lines 11 to 13 in 14a01eb

	At startup, if the option `--no-macaroons` is **not** used, a Bolt DB key/value
	store named `data/macaroons.db` is created with a bucket named `macrootkeys`.
	In this DB the following two key/value pairs are stored:

it mentions a Bolt DB, but we now have SQLite and Postgres DB types. We should clarify this to whatever is implemented right. Possibly we need to do more rework on the macaroon SQL DB though, so not sure what the terminal details here will be.