doc: update supported algorithms/mechanisms (#377)

Flame supports several algorithms/mechanisms. Those are listed as a
table.

README.md

@@ -38,6 +38,22 @@ flame
  └── scripts (utility scripts)
 ```
 
+## Supported Algorithms/Mechanisms
+
+| Method          | Note                                                                                                                               |
+|-----------------|------------------------------------------------------------------------------------------------------------------------------------|
+| FedAvg          | https://arxiv.org/pdf/1602.05629.pdf                                                                                               |
+| FedYogi         | https://arxiv.org/pdf/2003.00295.pdf                                                                                               |
+| FedAdam         | https://arxiv.org/pdf/2003.00295.pdf                                                                                               |
+| FedAdaGrad      | https://arxiv.org/pdf/2003.00295.pdf                                                                                               |
+| FedProx         | https://arxiv.org/pdf/1812.06127.pdf                                                                                               |
+| FedBuff         | Asynchronous FL (https://arxiv.org/pdf/2106.06639.pdf and https://arxiv.org/pdf/2111.04877.pdf); secure aggregation is excluded    |
+| FedDyn          | https://arxiv.org/pdf/2111.04263.pdf; under development                                                                            |
+| OORT            | https://arxiv.org/pdf/2010.06081.pdf; client selection algorithm / mechanism; experimental release                                 |
+| Hierarchical FL | https://arxiv.org/pdf/1905.06641.pdf; a simplified version where k<sub>2</sub> = 1; support both synchronous and asynchronous FL   |
+| Hybrid FL       | A hybrid approach to combine federated learning with ring-reduce; topology motivated from https://openreview.net/pdf?id=H0oaWl6THa |
+
+
 ## Documentation
 
 A full document can be found [here](docs/README.md). The document will be updated on a regular basis.