Add DiscordBM/DiscordLogger to loggers list

[MahdiBM]

Motivation:

Add DiscordBM to the loggers list.

The description is:

a Discord package containing a standalone DiscordLogger library

Please do tell if you think "standalone" seems misleading 🤔 I'm just trying to mention that users don't need to depend on the full package just for Discord-logging.

Resolves #256

Modifications:

Edit README logger-list table.

Result:

More awareness about existence of a Swift package capable of logging to Discord.

[swift-server-bot]

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[swift-server-bot]

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[swift-server-bot]

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[ktoso]

@swift-server-bot test this please

[ktoso]

@swift-server-bot test this please

[MahdiBM]

@ktoso I think we need another round of running tests here 👀

[ktoso]

Looks good now, thanks! Yep, we'll merge after the checks run

[ktoso]

@swift-server-bot test this please