support both mysql and postgres

weed/filer2/postgres/README.txt

@@ -0,0 +1,17 @@
+
+1. create "seaweedfs" database
+
+export PGHOME=/Library/PostgreSQL/10
+$PGHOME/bin/createdb --username=postgres --password seaweedfs
+
+2. create "filemeta" table
+$PGHOME/bin/psql --username=postgres --password seaweedfs
+
+CREATE TABLE IF NOT EXISTS filemeta (
+  dirhash     BIGINT,
+  name        VARCHAR(1000),
+  directory   VARCHAR(4096),
+  meta        bytea,
+  PRIMARY KEY (dirhash, name)
+);
+