doc: update docker.md to use 'chromadb' instead of 'chroma-core'

[dheerapat]

Description of changes

Summarize the changes made by this PR.

If run old docker command it will throw an error that repo not found, change repo from chroma-core to chromadb instead

Test plan

How are these changes tested?

repeat a step in documentation

Documentation Changes

Are all docstrings for user-facing APIs updated if required? Do we need to make documentation changes in the docs repository?