Document how to add a new provider

README.md

@@ -13,3 +13,33 @@ dotnet run
 
 On Windows, run the `./run.bat` file.
 
+### Adding Custom Providers
+
+File system providers are located at `./Camelotia.Services/Providers/`. To add a custom file system provider, you need to create a separate class and implement the [IProvider](https://github.com/worldbeater/Camelotia/blob/master/Camelotia.Services/Interfaces/IProvider.cs) interface. It'll get integrated into the UI automagically.
+
+```cs
+public interface IProvider
+{
+    string Size { get; }
+        
+    string Name { get; }
+        
+    string Description { get; }
+
+    Task<IEnumerable<FileModel>> Get(string path);
+
+    Task DownloadFile(string from, Stream to);
+        
+    Task UploadFile(string to, Stream from);
+        
+    IObservable<bool> IsAuthorized { get; }
+        
+    bool SupportsDirectAuth { get; }
+        
+    bool SupportsOAuth { get; }
+
+    Task DirectAuth(string login, string password);
+
+    Task OAuth();
+}
+```