ENH: Clean up lesson - Githubissues

Clean up lesson:

Remove contents in _episodes_md folder: the lesson contents being pulled at the Carpentries website are hosted in the _episodes folder.
Update the episode content table in the README file: add missing episodes, and update schedule and questions.

This cleanup is necessary for the transition to the new Carpentries Workbench infrastructure. Avoids the error:

Error: cannot open the connection
✖ There were issues with the lesson build process, see 'carpentries-incubator/SDC-BIDS-IntroMRI.err for details'
Warning messages:
1: In file(con, "r") :
  'raw = FALSE' but '/home/jhlegarreta/src/carp-transit-intromri/release/carpentries-incubator/SDC-BIDS-IntroMRI/_episodes_md' is not a regular file
2: In file(con, "r") :
  cannot open file '/home/jhlegarreta/src/carp-transit-intromri/release/carpentries-incubator/SDC-BIDS-IntroMRI/_episodes_md': it is a directory

at the

make release/carpentries-incubator/SDC-BIDS-IntroMRI.json

step.

See https://carpentries.github.io/sandpaper-docs/migrating-from-styles.html for the transition steps.

carpentries-incubator / SDC-BIDS-IntroMRI

ENH: Clean up lesson #41