README: Migration to Monorepo

[mandarini]

The Supabase JS repo has been converted to a monorepo, and all other JS client libs have been moved here.

All libraries are now released under a single version, starting 2.74.0.

Please read this Discussion here: Supabase JS Client Libs: Migration to Monorepo

[varunaswal]

Just confirming that @supabase/postgrest-js 1.21.4 -> 2.74.0 is just syncing the versions, not a major release?

[mandarini]

@varunaswal yes, that is correct! Thank you for pointing it out!