Document that non-Encryption SDK exceptions can be raised

The API documentation for the Python Encryption SDK lists [custom exception types](https://aws-encryption-sdk-python.readthedocs.io/en/latest/generated/aws_encryption_sdk.exceptions.html), but the APIs may let through exceptions from underlying libraries (e.g. `InvalidTag` and `InvalidSignature`) from pyca/cryptography. We should add a note to the documentation stating this.

Alternatively (or additionally) we can try to wrap these kind of exceptions into Encryption SDK custom exceptions with additional context.

从 Python Encryption SDK 的 API 文档和 issue 中链接的生成异常页面开始；检查当前如何描述自定义异常类型。完成标准是文档明确说明底层加密异常（例如 InvalidTag 和 InvalidSignature）可能会继续传播，除非项目选择将它们包装起来这一替代方案。

由索引模型根据 Issue 内容生成。