Now COPY '/data' folder, fix dynamic mode stuff, update comments

- need to copy contents of '/data' folder so that we can apply
  appropriate permissions to it later. The presence of a '/data' folder
  in the hub repository is now mandatory as `docker build` will fail if
  it's missing. This also agrees with the choice of `/data' as a default
  `cd` location for Supervisor. Fixes #4.
- spelling typos
- update instructions for '/data' folder inclusion
Exclude git repository from permissions changing
Typo in echo.