(docs) Remove snapshot field from snapshot table setup (#48)

The table uses `payload` instead.

Author: SeanKilleen

README.md

@@ -101,7 +101,6 @@ CREATE TABLE {your_snapshot_table_name} (
     created_at BIGINT NOT NULL,
     manifest VARCHAR(500) NOT NULL,
     payload BYTEA NOT NULL,
-    snapshot BYTEA NOT NULL,
     serializer_id INTEGER NULL,
     CONSTRAINT {your_snapshot_table_name}_pk PRIMARY KEY (persistence_id, sequence_nr)
 );