Update meilisearch.md

It seems the host defaulting as localhost has not worked for people in at least two instances

The documentation says to set as localhost whereas it seems to default to meilisearch and that does work

References:
https://misskey-doc.7ka.org/ja/misskey/enable-meilisearch
https://discord.com/channels/1126590789322035230/1163467816284991591/1291157680840507454
https://discord.com/channels/1126590789322035230/1163467816284991591/1281352518928175164