docs: Update "more options here" link in README

The "more options here" link pointed to an old Revolt.toml commit showing options which have since changed. Point to the main branch instead.

Signed-off-by: James Renken <james@renken.is>

README.md

@@ -148,7 +148,7 @@ chmod +x ./generate_config.sh
 ./generate_config.sh your.domain
 ```
 
-You can find [more options here](https://github.com/revoltchat/backend/blob/df074260196f5ed246e6360d8e81ece84d8d9549/crates/core/config/Revolt.toml), some noteworthy configuration options:
+You can find [more options here](https://github.com/revoltchat/backend/blob/main/crates/core/config/Revolt.toml), some noteworthy configuration options:
 
 - Email verification
 - Captcha