Revise TTS Docker directions to use Docker networking

[wired-filipino-owl]

Using host.docker.internal did not work for me to setup Kokoro-FastAPI. I assume this is a (somewhat) recent change to Docker.

I had to create a docker network and add Open-WebUI and Kokoro-FastAPI's containers to the network.

Rough directions (for already running containers):

#if your container names don't match, you can rename them to what you like using "docker rename <container id> <new container name>"
#you can get the id/names from "docker ps" or "docker container ls"
#create the Docker network (replace local-llm with whatever name you like)
docker network create local-llm
#add the containers to the network
docker network connect local-llm open-webui
docker network connect local-llm kokoro-fastapi
#restart the containers to get networking working properly
docker restart open-webui kokoro-fastapi

You can then access Kokoro via http://kokoro-fastapi:8880/v1 on Open-WebUI.

I would submit a PR for just Kokoro-FastAPI but I don't know how to use Docker Compose. I'm sure you could configure it to network the two containers.