Fix not-entirely-accurate comment about COPY FROM being "much faster"

lpsmith#3 (comment)

Performing INSERTs within a transaction block is much faster than without, but
is still slower than COPY.  Also, multiple rows can be inserted with a single
INSERT statement:

    INSERT INTO tablename (id, col1, col2) VALUES
        (1, 0, 1),
        (2, 1, 0),
        (3, 1, 1);

Database/PostgreSQL/LibPQ.hsc

@@ -1519,8 +1519,8 @@ unescapeBytea bs =
 -- $copyfrom
 --
 -- This provides support for PostgreSQL's @COPY FROM@ facility.  When inserting
--- rows in bulk, @COPY FROM@ is /much/ faster than individual @INSERT@
--- statements.
+-- rows in bulk, @COPY FROM@ is faster than individual @INSERT@ statements for
+-- each row.
 --
 -- For more information, see:
 --