Add eval config

eval.yaml

@@ -0,0 +1,13 @@
+name: TweetTopicSingleClassification
+description: Topic classification dataset on Twitter with 6 labels. Each instance
+  of TweetTopic comes with a timestamp which distributes from September 2019 to August
+  2021. Tweets were preprocessed before the annotation to normalize some artifacts,
+  converting URLs into a special token {{URL}} and non-verified usernames into {{USERNAME}}.
+  For verified usernames, we replace its display name (or account name) with symbols
+  {@}.
+evaluation_framework: mteb
+tasks:
+- id: TweetTopicSingleClassification
+- id: TweetTopicSingleClassification_default_test_2021
+  config: default
+  split: test_2021