Add documentation for JLD2 I/O

docs/src/man/importing_and_exporting.md

@@ -113,6 +113,28 @@ As you can see the code required to transform `iris` into a proper input to the
 format is not easy. Therefore CSV.jl is the preferred package to write CSV files
 for data stored in data frames.
 
+## JLD2 Files
+
+A convenient format for reading and writing data frames in JLD2, which saves and loads
+Julia data structures in a format comprising a subset of HDF5. Unlike several other 
+formats, JLD2 preserves custom Types. The `save` and `load` functions, provided by FileIO.jl, 
+allow to read/write a data frame from/to a JLD2 file.  
+
+A data frame can be saved as a JLD2 file output.jld2 using
+
+```julia
+using FileIO
+using Pkg; Pkg.add("JLD2")
+
+df = DataFrame(x=1, y=2)
+save("output.jld2", Dict("df" => df))
+```
+
+and can be read using
+```julia
+load("output.jld2") # -> Dict{String, Any} with 1 entry: "df" => 1×2 DataFrame
+```
+
 ## Other formats
 
 Other data formats are supported for reading and writing in the following packages