Add "md" source

[puripuri2100]

I have added "md" module.

ex.

(sources
   ((md "mdja.satysfi-md" "src/md/mdja.satysfi-md")))

[na4zagin3]

@puripuri2100 Thanks! Can you update testcase command_opam_install__library as well?

https://github.com/na4zagin3/satyrographos/blob/master/test/testcases/command_opam_install__library.ml#L14-L18 https://github.com/na4zagin3/satyrographos/blob/master/test/testcases/command_opam_install__library.ml#L45-49

[na4zagin3]

Oops, can you also update the snapshot (see https://dune.readthedocs.io/en/stable/tests.html for more details) with the following commands?

# Run test to ensure only command_opam_install__library is broken
$ dune test

# Update snapshots
$ dune promote

# Ensure all the tests pass 
$ dune test

# Check if only the snapshot for command_opam_install__library is updated
$ git status

[na4zagin3]

thanks!