Create readme.md

Bot/Handler/MusicPlayer/PlayCommand/readme.md

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+```mermaid
+flowchart LR
+    PlayHandler --> EnsureConnected
+    EnsureConnected --> GetPlayer
+    GetPlayer --> SearchAsync
+    SearchAsync --> SearchResponse
+    SearchResponse --> PlayTrack
+    PlayTrack --> NowPlayingEmbed
+```
+
+| Name | Description |
+|--|--|
+| PlayHandler | Holds the logic for playing songs |
+| GetPlayer | Joins voice channel, produces chat resposne |
+| EnsureConnected | Makes sure the client is connected |
+| SearchAsync | Searches for songs information |
+| SearchResponse | Handling possible errors from the response of SearchAsync |
+| PlayTrack | Plays the song |
+
+There is also OnTrackEnd, when it get called an attempt is made to play the next song in queue.