Update spatial_joins.md

docs/src/tutorials/spatial_joins.md

@@ -8,6 +8,7 @@ In this tutorial, we will show how to perform a spatial join on first a toy data
 
 In order to perform the spatial join, we use **[FlexiJoins.jl](https://github.com/JuliaAPlavin/FlexiJoins.jl)** to perform the join, specifically using its `by_pred` joining method.  This allows the user to specify a predicate in the following manner, for any kind of table join operation:
 ```julia
+using FlexiJoins
 innerjoin((table1, table1),
     by_pred(:table1_column, predicate_function, :table2_column) # & add other conditions here
 )