### Description
renamed several repository links from `hwchase17` to `langchain-ai`.
### Why
I discovered that the README file in the devcontainer contains an old
repository name, so I took the opportunity to rename the old repository
name in all files within the repository, excluding those that do not
require changes.
### Dependencies
none
### Tag maintainer
@baskaryan
### Twitter handle
[kzk_maeda](https://twitter.com/kzk_maeda)
**Description**
Fixes broken link to `CONTRIBUTING.md` in `libs/langchain/README.md`.
Because`libs/langchain/README.md` was copied from the top level README,
and because the README contains a link to `.github/CONTRIBUTING.md`, the
copied README's link relative path must be updated. This commit fixes
that link.
Erick Friis