cross reference fix

Author: TorkelE

docs/src/introduction_to_catalyst/introduction_to_catalyst.md

@@ -44,7 +44,7 @@ listed chemical species and unknowns. [`@reaction_network`](@ref) returns a
 [`ReactionSystem`](@ref), which we saved in the `repressilator` variable. It can
 be converted to a variety of other mathematical models represented as
 `ModelingToolkit.AbstractSystem`s, or analyzed in various ways using the
-[Catalyst.jl API](@ref). For example, to see the chemical species, parameters,
+[Catalyst.jl API](@ref api). For example, to see the chemical species, parameters,
 and reactions we can use
 ```@example tut1
 species(repressilator)

docs/src/model_creation/programmatic_CRN_construction.md

@@ -180,7 +180,7 @@ This ensured they were properly treated as species and not parameters. See the
 
 ## Basic querying of `ReactionSystems`
 
-The [Catalyst.jl API](@ref) provides a large variety of functionality for
+The [Catalyst.jl API](@ref api) provides a large variety of functionality for
 querying properties of a reaction network. Here we go over a few of the most
 useful basic functions. Given the `repressillator` defined above we have that
 ```@example ex
@@ -247,5 +247,5 @@ rx1.prodstoich
 rx1.netstoich
 ```
 
-See the [Catalyst.jl API](@ref) for much more detail on the various querying and
+See the [Catalyst.jl API](@ref api) for much more detail on the various querying and
 analysis functions provided by Catalyst.