added some docstrings

src/axioms.jl

@@ -351,6 +351,32 @@ struct Constant{S<:String,D,V}
     value::V
 end
 
+"""
+    Constant(constant::Dict{String, Any}) -> Constant
+
+Create a `Constant` object from a dictionary.
+
+# Arguments
+
+  - `constant::Dict{String, Any}`: A dictionary containing the following keys:
+
+      + `"description"`: Description of the constant.
+      + `"short_name"`: Short name of the constant.
+      + `"default"`: Default value of the constant.
+
+# Returns
+
+  - `Constant`: An instance of the `Constant` struct with fields populated based on the provided dictionary.
+
+# Example
+
+```julia
+constant_dict = Dict(
+    "description" => "Speed of light in vacuum", "short_name" => "c", "default" => 299792458
+)
+constant = Constant(constant_dict)
+```
+"""
 function Constant(constant::Dict{String,Any})
     description = constant["description"]
     short_name = constant["short_name"]