[MISC] Adding Dimitri Papadopoulos Orfanos to the list of contributors

[DimitriPapadopoulos]

As suggested by @chrisfilo in #155.

[chrisgorgo]

Please add your github username to CODEOWNER (see rule 3 at https://github.com/bids-standard/bids-specification/blob/master/DECISION-MAKING.md#rules).

[DimitriPapadopoulos]

This CODEOWNER file is almost empty, I can only find @chrisfilo is in it. I had had a look at the DECISION-MAKING document but the CODEOWNER file itself tells a different story:

This files [...] merely serves the purpose of notifying interested contributors when a new Pull Request that proposes changes to a particular file is submitted. If you would like to subscribe to such notifications (in a form of a Request for Review) please add your github username next to the file you want to monitor below.

[chrisgorgo]

The rules are new - that's why the file is so empty.

Rule 3 was suggested by @choldgraf to incentivize people to add their names to CODEOWNERS, get automatic review invites and hopefully review more PRs.

[DimitriPapadopoulos]

Can I add my name to an existing line or do I need to create a new line?

To be more specific, is the following line legal?

/src/01-common-principles.md @chrisfilo @DimitriPapadopoulos 

Or should I create a new line?

/src/01-common-principles.md @chrisfilo
/src/01-common-principles.md @DimitriPapadopoulos 

[chrisgorgo]

You can add your name to an existing line. More details at https://help.github.com/en/articles/about-code-owners

Thanks!

[DimitriPapadopoulos]

I have added myself to CODEOWNERS.