Add a brief description to the README

Because
* Even though the tutorial is not uploaded, someone may want to install
the package.

README.md

@@ -5,3 +5,14 @@
 [![Build Status](https://github.com/pmc4/VectorPlotDigitizer.jl/actions/workflows/CI.yml/badge.svg?branch=main)](https://github.com/pmc4/VectorPlotDigitizer.jl/actions/workflows/CI.yml?query=branch%3Amain)
 [![Coverage](https://codecov.io/gh/pmc4/VectorPlotDigitizer.jl/branch/main/graph/badge.svg)](https://codecov.io/gh/pmc4/VectorPlotDigitizer.jl)
 [![Aqua](https://raw.githubusercontent.com/JuliaTesting/Aqua.jl/master/badge.svg)](https://github.com/JuliaTesting/Aqua.jl)
+
+WIP package. Documentation and tutorials will be upload it in the future, sorry for the inconvenience.
+
+The idea of VectorPlotDigitizer is to be able to digitize the data of plots that are given in a vector format, such as SVG or PDF.
+
+To install it enter Pkg mode in a Julia terminal by writing `]` and write `add VectorPlotDigitizer` or use
+
+```julia
+using Pkg
+Pkg.add(VectorPlotDigitizer)
+```