Change README.md (#242)

Remove PG10 from README.md and add PG15. 
Corrected PGBASE to PGDATA

README.md

@@ -14,12 +14,12 @@ different PostgreSQL server versions without introducing server version
 check code blocks.  Please choose a branch to match the PostgreSQL version
 you will be building pg_rman against.
 
-* master : branch for PostgreSQL 15beta [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=master&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
+* master : branch for PostgreSQL 15 [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=master&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
+* REL_15_STABLE : branch for PostgreSQL 15 [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=master&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
 * REL_14_STABLE : branch for PostgreSQL 14 [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=REL_14_STABLE&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
 * REL_13_STABLE : branch for PostgreSQL 13 [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=REL_13_STABLE&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
 * REL_12_STABLE : branch for PostgreSQL 12 [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=REL_12_STABLE&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
 * REL_11_STABLE : branch for PostgreSQL 11 [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=REL_11_STABLE&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
-* REL_10_STABLE : branch for PostgreSQL 10 [![Test](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml/badge.svg?branch=REL_10_STABLE&event=push)](https://github.com/ossc-db/pg_rman/actions/workflows/build.yml)
 
 How to use
 ----------
@@ -65,7 +65,7 @@ recovery_target_timeline = '1'
 $ pg_ctl start
 ````
 
-After to PostgreSQL12, note that pg_rman itself added PostgreSQL PITR related options to `postgresql.conf` file and generates the `recovery.signal` file in sub directory of PGBASE
+After to PostgreSQL12, note that pg_rman itself added PostgreSQL PITR related options to `postgresql.conf` file and generates the `recovery.signal` file in $PGDATA.
 
 To see more options to use with each command, run `pg_rman --help`.