[Docs] Refine the docstring of EvalHook (#2576)

* 📃

 docs(hooks): EvalHook comments

Refine the EvalHook comments

* Refine comments EvalHook

Update mmcv/runner/hooks/evaluation.py
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* 📃

 docs(Hooks): update Eval Hook

Slove line too long

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Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

mmcv/runner/hooks/evaluation.py

@@ -23,10 +23,10 @@ class EvalHook(Hook):
     Args:
         dataloader (DataLoader): A PyTorch dataloader, whose dataset has
             implemented ``evaluate`` function.
-        start (int | None, optional): Evaluation starting epoch. It enables
-            evaluation before the training starts if ``start`` <= the resuming
-            epoch. If None, whether to evaluate is merely decided by
-            ``interval``. Default: None.
+        start (int | None, optional): Evaluation starting epoch or iteration.
+            It enables evaluation before the training starts if ``start`` <=
+            the resuming epoch or iteration. If None, whether to evaluate is
+            merely decided by ``interval``. Default: None.
         interval (int): Evaluation interval. Default: 1.
         by_epoch (bool): Determine perform evaluation by epoch or by iteration.
             If set to True, it will perform by epoch. Otherwise, by iteration.