To load a csv file into a table, one way to do it is to use the docker cp command to copy the file into the container. You can then run the \copy command from a cmd line in the container.
docker cp ./projects.csv some-postgres:/projects.csv
docker exec -it some-postgres psql -U postgres
** from psql:
postgres=# \copy projects(id,project_name,description) from '/projects.csv' csv header;