docs: Updated WikipediaLoader documentation (#25647)
- Output of the cells was not included in the documentation. I have
added them.
- There is another parameter in the `WikipediaLoader` class called
`doc_content_chars_max` (Based on
[this](https://api.python.langchain.com/en/latest/document_loaders/langchain_community.document_loaders.wikipedia.WikipediaLoader.html)).
I have included this in the list of parameters.
- I put the list of parameters under a new section called "Parameters"
in the documentation.
- I also included the `langchain_community` package in the installation
command.
- Some minor formatting/spelling issues were fixed.
