Added docs for enabling extension

README.md

@@ -14,10 +14,16 @@ Follow the instructions for your database library:
 
 ## DBD::Pg
 
+Enable the extension
+
+```perl
+$dbh->do('CREATE EXTENSION IF NOT EXISTS vector');
+```
+
 Create a table
 
 ```perl
-$dbh->do('CREATE TABLE items (embedding vector(3))');
+$dbh->do('CREATE TABLE items (id bigserial PRIMARY KEY, embedding vector(3))');
 ```
 
 Insert vectors
@@ -41,7 +47,7 @@ my $sth = $dbh->prepare('SELECT * FROM items ORDER BY embedding <-> $1 LIMIT 5')
 my @embedding = (1, 1, 1);
 $sth->execute(vector(\@embedding));
 while (my @row = $sth->fetchrow_array()) {
-    print($row[0] . "\n");
+    print($row[1] . "\n");
 }
 ```
 

example.pl

@@ -4,7 +4,7 @@
 
 $dbh->do('CREATE EXTENSION IF NOT EXISTS vector');
 $dbh->do('DROP TABLE IF EXISTS items');
-$dbh->do('CREATE TABLE items (embedding vector(3))');
+$dbh->do('CREATE TABLE items (id bigserial PRIMARY KEY, embedding vector(3))');
 
 sub vector {
     return '[' . join(',', @{$_[0]}) . ']';
@@ -20,7 +20,7 @@ sub vector {
 my @embedding = (1, 1, 1);
 $sth->execute(vector(\@embedding));
 while (my @row = $sth->fetchrow_array()) {
-    print($row[0] . "\n");
+    print($row[1] . "\n");
 }
 
 $dbh->do('CREATE INDEX my_index ON items USING ivfflat (embedding vector_l2_ops)');