ENH - added placeholder page and link

[schoffelen]

@jiecui please add your documentation here.

[schoffelen]

This could be a link to your (updated) README.md file in the mef_reader_fieldtrip repo

[robertoostenveld]

@jiecui are you still planning to add some documentation regarding MEF to the fieldtrip website? If not, I suggest we close this pull request.