add tidal docs

docs/tidal.md

@@ -0,0 +1,31 @@
+## Tidal to Deezer
+
+`d-fi-core` exports Tidal api to easily convert tracks, albums, artists and playlist to deezer via matching ISRC and UPC code.
+
+## Usage
+
+Here's a simple example. All method returns `Object` or throws `Error`. Make sure to catch error on your side.
+
+```ts
+import {tidal} from 'd-fi-core';
+
+// Convert single track to deezer
+const track = await tidal.track2deezer(song_id);
+console.log(track);
+
+// Convert album and tracks to deezer
+const [album, tracks] = await tidal.album2deezer(album_id);
+console.log(album);
+console.log(tracks);
+
+// Convert playlist and tracks to deezer
+const [playlist, tracks] = await tidal.playlist2Deezer(playlist_id);
+console.log(playlist);
+console.log(tracks);
+
+// Convert artist tracks to deezer (limited to 10 tracks)
+const tracks = await tidal.artist2Deezer(artist_id);
+console.log(tracks);
+```
+
+There are more methods available. Take a look at [`src/converter/tidal.ts`](https://github.com/d-fi/d-fi-core/blob/master/src/converter/tidal.ts) and [`__tests__/converter/tidal.ts`](https://github.com/d-fi/d-fi-core/blob/master/__tests__/converter/tidal.ts) to understand more.