Add aloha + improve readme

lerobot/common/datasets/aloha.py

@@ -124,8 +124,8 @@ class AlohaExperienceReplay(AbstractExperienceReplay):
     def image_keys(self) -> list:
         return [("observation", "image", cam) for cam in CAMERAS[self.dataset_id]]
 
-    def _download_and_preproc(self):
-        raw_dir = self.data_dir.parent / f"{self.data_dir.name}_raw"
+    def _download_and_preproc_obsolete(self, data_dir="data"):
+        raw_dir = Path(data_dir) / f"{self.dataset_id}_raw"
         if not raw_dir.is_dir():
             download(raw_dir, self.dataset_id)
 
@@ -174,7 +174,9 @@ class AlohaExperienceReplay(AbstractExperienceReplay):
 
                 if ep_id == 0:
                     # hack to initialize tensordict data structure to store episodes
-                    td_data = ep_td[0].expand(total_num_frames).memmap_like(self.data_dir)
+                    td_data = (
+                        ep_td[0].expand(total_num_frames).memmap_like(Path(self.root) / f"{self.dataset_id}")
+                    )
 
                 td_data[idxtd : idxtd + len(ep_td)] = ep_td
                 idxtd = idxtd + len(ep_td)