chore: release v6.0.0 (#4)

* chore: release v6.0.0

* docs: document the 6.0.0 breaking changes

cargo-semver-checks flagged four major-breaking changes in soulseek-rs-lib,
none of which carried a `!` or BREAKING CHANGE footer, so the generated
changelog had no migration note for a major bump.

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Michel de Graaf <michel@re-invention.nl>

Cargo.lock

@@ -2407,7 +2407,7 @@ checksum = "8ed6a63f02c8539c91a8685a86f4099661ba3da017932f6ebbea6de3f0fa7c90"
 
 [[package]]
 name = "soulseek-rs"
-version = "5.0.0"
+version = "6.0.0"
 dependencies = [
  "clap",
  "color-eyre",
@@ -2425,7 +2425,7 @@ dependencies = [
 
 [[package]]
 name = "soulseek-rs-lib"
-version = "5.0.0"
+version = "6.0.0"
 
 [[package]]
 name = "stable_deref_trait"