Update docs (#71)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/reference/base_trainer.md

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+All task Trainers are inherited from `BaseTrainer` class that contains the model training and optimzation routine boilerplate. You can override any function of these Trainers to suit your needs.
+
+---
+### BaseTrainer API Reference
+:::ultralytics.yolo.engine.trainer.BaseTrainer

docs/reference/model.md

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+::: ultralytics.yolo.engine.model