docs(intro): show how to list allowed subsolvers for trunk/tron least-squares variants

Author: arnavk23

tutorials/introduction-to-jsosolvers/index.jmd

@@ -46,6 +46,13 @@ The solvers `tron` and `trunk` both have a specialized implementation for input
 
 The following examples illustrate this specialization.
 
+To list the allowed least-squares subsolvers for these specializations:
+
+```julia
+JSOSolvers.trunkls_allowed_subsolvers
+JSOSolvers.tronls_allowed_subsolvers
+```
+
 ```julia
 using JSOSolvers, ADNLPModels
 f(x) = (x[1] - 1)^2 + 4 * (x[2] - x[1]^2)^2