Fix typo.

README.md

@@ -123,7 +123,7 @@ For large data sets (millions of rows to index), the "compatible" storage
 used by default will typically no longer be enough to keep the index small
 enough.
 
-Users have reported **major improvements** (2 order of magniture) when turning
+Users have reported **major improvements** (2 order of magnitude) when turning
 the `owner_type` and `fuzzy_field` columns of the `trigrams` table from
 `VARCHAR` (the default) into `ENUM`. This is particularly efficient with
 MySQL and pgSQL.