docs: use “An” before words that start with vowel (#92)

Author: xayanide

README.md

@@ -1,6 +1,6 @@
 <a href="https://github.com/KagChi/noteblock"> <img align="right" src="https://cdn.discordapp.com/avatars/584333920875708426/8a4ed8376a2c612e30270783b74b6901.jpg?size=2048" width="150"></a>
 
-> [@noteblock](https://github.com/KagChi/noteblock) (A open-source music bot based on lavalink.) 🤖: Version: 1.3.0.
+> [@noteblock](https://github.com/KagChi/noteblock) (An open-source music bot based on lavalink.) 🤖: Version: 1.3.0.
 
 🎵 | Listen to a music with style! Feature rich with high quality music from YouTube/Soundcloud.