Improvements to the docker build + update readme

docker/deepspeed/Dockerfile

@@ -1,6 +1,6 @@
-ARG GITHUB_REPOSITORY
+ARG DOCKER_REPOSITORY
 ARG DOCKER_TAG=latest
-FROM ${GITHUB_REPOSITORY}alltalk_tts_environment:${DOCKER_TAG}
+FROM ${DOCKER_REPOSITORY}alltalk_tts_environment:${DOCKER_TAG}
 
 ARG DEEPSPEED_VERSION=0.16.3
 ENV DEEPSPEED_VERSION=$DEEPSPEED_VERSION