message: add comment about psql LIKE index usage
diff: @@ -58,8 +58,11 @@ pub fn sitemap_handler(req: &mut Request) -> IronResult<Response> {
  GROUP BY crates.name
  ",
  &[
  - // this LIKE pattern has the '%' only at the end,
  - // so postgres can use the index on `name`
  + // postgres can use the normal BTREE index on `name`
  + // for LIKE queries, if they are anchored to the
  + // beginning of the string.
  + // This does not work for ILIKE and alphabetic
  + // characters, hence the OR.
  &format!("{}%", letter),
  &format!("{}%", letter.to_uppercase()),
  ],
  