README typo and missing link for Kotlin implementation

[ysandeepkumarreddy]

Hi maintainers 👋

I noticed an inconsistency and a broken link in the README related to the Kotlin implementation.

Description

In the Other S2 implementations section, the README mentions a Kotlin implementation, but the link currently results in a 404 / repository not found, making the Kotlin source unreachable

This can be confusing for users looking specifically for the Kotlin version.

README reference (quoted)

Other S2 implementations
Go (Approximately 40% complete.)
Java
Kotlin (Complete except binary serialization)