References to gitbook pages broken in ~/README.md

[twallema]

Description of issue

All references to the Gitbook documentation (paragraph starting with "This documentation is organized as follows. [...].") are broken in the main readme file (~/README.md). All other references work.

Proposed fix

Using model-description.md as an example.

Change

The [Model Description](model-of-disease-transmission-+-observation/model-description.md) section describes the mathematical framework [...]

into

The [Model Description](gitbook/gempyor/model-description.md) section describes the mathematical framework [...]