Yes, I think you're right - we'll make sure to add a screencast for the next release.
The procedure for 1D interpolation is the following:
- Load a point map with the data of the known points (e.g., gauging stations) to the maps panel.
- Load a line map with the 1D geometry (e.g., river).
- Use Link to parameter on the point map and link to the corresponding boundary condition.
- In the link properties, choose the line map as the selection map.
- Also in the link properties, choose 1D Linear Interpolation as the interpolation method.