Fix for rag-supabase readme (langchain-ai#12869)

- **Description:** Correct naming for package in README
- **Issue:** README wasn't aligned with pyproject.toml, resulting in not
being able to install the rag-supabase package.
  - **Tag maintainer:** @gregnr

Author: jasanfarah

templates/rag-supabase/README.md

@@ -82,13 +82,13 @@ pip install -U langchain-cli
 To create a new LangChain project and install this as the only package, you can do:
 
 ```shell
-langchain app new my-app --package rag_supabase
+langchain app new my-app --package rag-supabase
 ```
 
 If you want to add this to an existing project, you can just run:
 
 ```shell
-langchain app add rag_supabase
+langchain app add rag-supabase
 ```
 
 And add the following code to your `server.py` file:
@@ -127,7 +127,7 @@ We can access the template from code with:
 ```python
 from langserve.client import RemoteRunnable
 
-runnable = RemoteRunnable("http://localhost:8000/rag_supabase")
+runnable = RemoteRunnable("http://localhost:8000/rag-supabase")
 ```
 
 TODO: Add details about setting up the Supabase database