Add more info and example

Author: aurorarossi

src/datasets/graphs/chickenpox.jl

@@ -60,17 +60,36 @@ The ChickenPox dataset contains county-level chickenpox cases in Hungary between
 
 `ChickenPox` is composed of a graph with nodes representing counties and edges representing the neighborhoods, and a metadata dictionary containing the correspondence between the node indices and the county names. 
 
-The node features are the number of weekly chickenpox cases in each county.
+The node features are the number of weekly chickenpox cases in each county. They are represented as an array of arrays of size `(1, num_nodes, num_timesteps_in)`. The target values are the number of weekly chickenpox cases in each county. They are represented as an array of arrays of size `(1, num_nodes, num_timesteps_out)`. In both cases. two consecutive arrays are shifted by one-time step.
 
 The dataset was taken from the [Pytorch Geometric Temporal repository](https://pytorch-geometric-temporal.readthedocs.io/en/latest/modules/dataset.html#torch_geometric_temporal.dataset.chickenpox.ChickenpoxDatasetLoader) and more information about the dataset can be found in the paper ["Chickenpox Cases in Hungary: a Benchmark Dataset for
 Spatiotemporal Signal Processing with Graph Neural Networks"](https://arxiv.org/pdf/2102.08100).
 
 
 # Keyword Arguments
 - `normalize::Bool`: Whether to normalize the data using Z-score normalization. Default is `true`.
-- `num_timesteps_in::Int`: The number of time steps for the input features. Default is `8`.
-- `num_timesteps_out::Int`: The number of time steps for the target values. Default is `8`.
+- `num_timesteps_in::Int`: The number of time steps, in this case, the number of weeks, for the input features. Default is `8`.
+- `num_timesteps_out::Int`: The number of time steps, in this case, the number of weeks, for the target values. Default is `8`.
 - `dir::String`: The directory to save the dataset. Default is `nothing`.
+
+# Examples
+```julia-repl
+julia> using JSON3 # import JSON3
+
+julia> dataset = ChickenPox()
+dataset ChickenPox:
+  metadata  =>    Dict{Symbol, Any} with 20 entries
+  graphs    =>    1-element Vector{MLDatasets.Graph}
+
+julia> dataset.graphs[1].num_nodes # 20 counties
+20
+
+julia> size(dataset.graphs[1].node_data.features[1]) 
+(1, 20, 8)
+
+julia> dataset.metadata[:BUDAPEST] # The node 5 correponds to Budapest county 
+5
+```
 """
 struct ChickenPox <: AbstractDataset
     metadata::Dict{Symbol, Any}