Add examples and change readme to reduce dependency on langchain docs

[VarinThakur01]

Till our PR gets merged for adding documentation on the langchain's documentation website, we point the users of the package to refer to the examples/ directory to see the usage of different components.

The readme is also updated accordingly to point to the directory for the usage examples.

[yonarw]

Nice. This way we can at least keep our docs up to date.
Is there a way to automatically run the notebooks though CI before a new release to make sure docs are always valid?

[VarinThakur01]

Nice. This way we can at least keep our docs up to date. Is there a way to automatically run the notebooks though CI before a new release to make sure docs are always valid?

We will handle this in a different PR.