Added oneliner to README

Author: mattiasvillani

README.md

@@ -1,6 +1,7 @@
 # TimeSeriesUtils
 
-[![Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://mattiasvillani.github.io/TimeSeriesUtils.jl/stable/)
 [![Dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://mattiasvillani.github.io/TimeSeriesUtils.jl/dev/)
 [![Build Status](https://github.com/mattiasvillani/TimeSeriesUtils.jl/actions/workflows/CI.yml/badge.svg?branch=main)](https://github.com/mattiasvillani/TimeSeriesUtils.jl/actions/workflows/CI.yml?query=branch%3Amain)
 [![Coverage](https://codecov.io/gh/mattiasvillani/TimeSeriesUtils.jl/branch/main/graph/badge.svg)](https://codecov.io/gh/mattiasvillani/TimeSeriesUtils.jl)
+
+Some utility functions for working with time series data in Julia, ARIMA tools and spectral density estimation.