add docstring to type struct

src/problems.jl

@@ -81,12 +81,26 @@ function isempty(assembly::Assembly)
     return T
 end
 
+"""
+Defines types for Problem variables.
+
+# Examples
+
+The type of 'elements' is Vector{Element}
+
+Add elements into the Problem element list.
+```@example
+a = [1, 2, 3]
+Problem.elements = a
+```
+
+"""
 type Problem{P<:AbstractProblem}
-    name :: AbstractString           # descriptive name for problem
+    name :: AbstractString           # descriptive name for the problem
     dimension :: Int                 # degrees of freedom per node
-    parent_field_name :: AbstractString # (optional) name of parent field e.g. "displacement"
+    parent_field_name :: AbstractString # (optional) name of the parent field e.g. "displacement"
     elements :: Vector{Element}
-    dofmap :: Dict{Element, Vector{Int64}} # connects element local dofs to global dofs
+    dofmap :: Dict{Element, Vector{Int64}} # connects the element local dofs to the global dofs
     assembly :: Assembly
     fields :: Dict{AbstractString, Field}
     postprocess_fields :: Vector{String}