community: Make doctran synchronous (#15264)
### Description
I found that the methods in [the doctran
library](https://github.com/psychic-api/doctran) have been restructured
into [synchronized
versions](https://github.com/psychic-api/doctran/commit/14944a59f7513b51e629a850e0de5ae276eabed9),
And [the example
ipynb](https://github.com/psychic-api/doctran/blob/main/examples.ipynb)
also shows that the code is synchronized, but the README has not been
updated yet.
so we need to modify the code and update the documentation.
### Issue
https://github.com/langchain-ai/langchain/issues/14645
