Make target `update_doc_table` has incorrect description

[ckadner]

The description of the Make target update_doc_table: ## Check markdown files for invalid links is incorrect (failed to update after copy/paste in PR #317)

https://github.com/machine-learning-exchange/mlx/blob/605fe331d863e62e770607130041d298268b4122/Makefile#L30-L31

It should read ## Regenerate the /docs/README.md file

.PHONY: update_doc_table
update_doc_table: ## Regenerate the /docs/README.md file

The descriptions of the Make targets can be viewed when running make help (or just make without specifying a target)

$ make

help                      List the Make targets with description
check_npm_packages        Verify NPM packages
update_npm_packages       Update NPM packages
check_doc_links           Check markdown files for invalid links
update_doc_table          Regenerate the /docs/README.md file
check_license             Make sure source files have license header

[ezinneanne]

Hello can I take this

[ckadner]

Hi @ezinneanne -- yes, please go ahead and submit a PR for this. Thank you!

[ckadner]

Closed via #329