Update README.md

#50 added DOI for library

README.md

@@ -16,6 +16,7 @@
 [![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/alenrajsp/tcxreader.svg)](http://isitmaintained.com/project/alenrajsp/tcxreader "Average time to resolve an issue")
 [![Percentage of issues still open](http://isitmaintained.com/badge/open/alenrajsp/tcxreader.svg)](http://isitmaintained.com/project/alenrajsp/tcxreader "Percentage of issues still open")
 [![All Contributors](https://img.shields.io/github/all-contributors/alenrajsp/tcxreader?color=ee8449&style=flat-square)](#contributors)
+[![DOI](https://zenodo.org/badge/317671425.svg)](https://zenodo.org/doi/10.5281/zenodo.10940281)
 
 ## Objective