iframe app doku

[janCstoffregen]

• The app is described for a researcher here: https://github.com/nie-ine/inseri/tree/2020-10/Tutorials/App%20descriptions%20for%20Researchers
• There is a link in the README to the external repository if applicable (for instance to https://www.primefaces.org/primeng/showcase/#/editor for the text editor)
• The functions and the variables in the code is either self explaining or have a comment above them
• The link to the description is included here: https://github.com/nie-ine/inseri/blob/2020-10/src/app/user-action-engine/mongodb/page/open-apps.model.ts#L172 (we need this so that the user gets to the description directly from the app)
• It has been reviewed by @domsteinbach

@GerhardLauer fyi