added crossJoin overload

- also added docs

docs/database/query-builder.mdx

@@ -250,6 +250,14 @@ If you would like to perform a "left join" or "right join" instead of an "inner
                      ->rightJoin("posts", "users.id", "=", "posts.user_id")
                      .get();
 
+#### Cross Join Clause
+
+You may use the `crossJoin` method to perform a "cross join". Cross joins generate a cartesian product between the first table and the joined table:
+
+    auto sizes = DB::table("sizes")
+                     ->crossJoin("colors")
+                     .get();
+
 #### Advanced Join Clauses
 
 You may also specify more advanced join clauses. To get started, pass a lambda expression as the second argument to the `join` method. The lambda expression will receive a `Orm::Query::JoinClause` instance which allows you to specify constraints on the "join" clause:

include/orm/query/querybuilder.hpp

@@ -238,6 +238,9 @@ namespace Orm::Query
         template<JoinTable T>
         inline Builder &
         crossJoin(T &&table, const std::function<void(JoinClause &)> &callback);
+        /*! Add a "cross join" clause to the query. */
+        template<JoinTable T>
+        inline Builder &crossJoin(T &&table);
 
         /*! Add a subquery join clause to the query. */
         template<SubQuery T>
@@ -928,6 +931,16 @@ namespace Orm::Query
         return join(table, callback, CROSS);
     }
 
+    template<JoinTable T>
+    Builder &
+    Builder::crossJoin(T &&table)
+    {
+        // No need to call joinInternal() because no bindings
+        m_joins.append(newJoinClause(*this, CROSS, std::forward<T>(table)));
+
+        return *this;
+    }
+
     template<SubQuery T>
     Builder &
     Builder::joinSub(T &&query, const QString &as, const QString &first,