doc/tutorial: fix typos

doc/tutorial/basics/aliases.md

@@ -8,7 +8,7 @@ An alias defines a local macro.
 
 A typical use case is to provide access to a shadowed field.
 
-Alias are not members of a struct. They can be referred to only within the
+Aliases are not members of a struct. They can be referred to only within the
 struct, and they do not appear in the output.
 
 <!-- CUE editor -->

doc/tutorial/basics/sumstruct.md

@@ -4,7 +4,7 @@ _Types ~~and~~ are Values_
 
 # Disjunctions of Structs
 
-Disjunction work for any type.
+Disjunctions work for any type.
 
 In this example we see that a `floor` of some specific house
 has an exit on level 0 and 1, but not on any other floor.