Readme: add reference to ptrack extension

Author: gsmolk

README.md

@@ -40,8 +40,9 @@ Regardless of the chosen backup type, all backups taken with `pg_probackup` supp
 
 `PTRACK` backup support provided via following options:
 * vanilla PostgreSQL compiled with ptrack patch. Currently there are patches for [PostgreSQL 9.6](https://gist.githubusercontent.com/gsmol/5b615c971dfd461c76ef41a118ff4d97/raw/e471251983f14e980041f43bea7709b8246f4178/ptrack_9.6.6_v1.5.patch) and [PostgreSQL 10](https://gist.githubusercontent.com/gsmol/be8ee2a132b88463821021fd910d960e/raw/de24f9499f4f314a4a3e5fae5ed4edb945964df8/ptrack_10.1_v1.5.patch)
-* Postgres Pro Standard 9.6, 10, 11
-* Postgres Pro Enterprise 9.6, 10, 11
+* vanilla PostgreSQL 12 with [ptrack extension](https://github.com/postgrespro/ptrack)
+* Postgres Pro Standard 9.6, 10, 11, 12
+* Postgres Pro Enterprise 9.6, 10, 11, 12
 
 ## Limitations