fixes types documentation

docs/src/types.md

@@ -26,6 +26,7 @@ We use [Nemo](https://www.nemocas.org/index.html)'s multivariate polynomial
 ring structures:
 
 ```@repl
+using AlgebraicSolving
 R, (x,y,z) = polynomial_ring(QQ, ["x", "y", "z"], ordering=:degrevlex)
 ```
 The above example defines a multivariate polynomial ring in three variables `x`, 
@@ -34,6 +35,7 @@ for printing polynomials in the following. One can also define polynomial rings
 over finite fields:
 
 ```@repl
+using AlgebraicSolving
 R, (x,y,z) = polynomial_ring(GF(101), ["x", "y", "z"], ordering=:degrevlex)
 ```
 
@@ -44,6 +46,7 @@ data structures connected to ideals in order to make computational algebra more
 effective:
 
 ```@repl
+using AlgebraicSolving
 R, (x,y,z) = polynomial_ring(QQ, ["x", "y", "z"], ordering=:degrevlex)
 I = Ideal([x+y+1, y*z^2-13*y^2])
 ```