Update tasks README with pisa task

Author: HallerPatrick

lm_eval/tasks/README.md

@@ -148,6 +148,8 @@ provided to the individual README.md files for each subfolder.
 | [pile](pile/README.md)                                                   | Open source language modelling data set that consists of 22 smaller, high-quality datasets.                                                                                                                                                                                                                                            | English                                                                                                                                                                                                                                                       |
 | [pile_10k](pile_10k/README.md)                                           | The first 10K elements of The Pile, useful for debugging models trained on it.                                                                                                                                                                                                                                                         | English                                                                                                                                                                                                                                                       |
 | [piqa](piqa/README.md)                                                   | Physical Interaction Question Answering tasks to test physical commonsense reasoning.                                                                                                                                                                                                                                                  | English                                                                                                                                                                                                                                                       |
+| [pisa](pisa/README.md)                                                   | Multi-lingual, mulit-model tasks that involve reading comprehension and math challenges.                                                                                                                                                                                                                                               | English, German, French, Spanish, Italien, Chinese.                                                                                                                                                                                                           |
+
 | [polemo2](polemo2/README.md)                                             | Sentiment analysis and emotion detection tasks based on Polish language data.                                                                                                                                                                                                                                                          | Polish                                                                                                                                                                                                                                                        |
 | [portuguese_bench](portuguese_bench/README.md)                           | Collection of tasks in European Portuguese encompassing various evaluation areas.                                                                                                                                                                                                                                                      | Portuguese                                                                                                                                                                                                                                                    |
 | [prost](prost/README.md)                                                 | Tasks requiring understanding of professional standards and ethics in various domains.                                                                                                                                                                                                                                                 | English                                                                                                                                                                                                                                                       |