README updated

Workflow badge added

Author: pedrolcl

README.md

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 Drumstick Multiplatform MIDI File Player
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+[![Build on Linux](https://github.com/pedrolcl/dmidiplayer/actions/workflows/linux-build.yml/badge.svg)](https://github.com/pedrolcl/dmidiplayer/actions/workflows/linux-build.yml)
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 This application is a multiplatform MIDI file player for Linux, Windows and macOS. It reads .MID (Standard MIDI Files), .KAR (Karaoke), and .WRK (Cakewalk) file formats, and outputs MIDI events to hardware MIDI ports and also software synths.
 
 [Drumstick](https://drumstick.sourceforge.io/docs/index.html) is a set of GPLv3 licensed C++/Qt libraries for MIDI applications. The project includes several tools as examples, and among them is the drumstick-guiplayer utility that leverages the Drumstick::ALSA library, so it is available only for Linux (because the ALSA sequencer is a linux only technology). Some people have requested a program with the same functionalities on Windows and macOS, and here it is. But this program is much more than that, and also works on Linux ...