Update documentation for v0.7

[jank324]

Needs to be done for #165. Should update the README and the example notebooks. Can only be done after #213.

[jank324]

#208 and #213 need to be merged before this can be fixed.

[Hespe]

I think the last line of the current README example is wrong. The argument has been renamed to incoming.

cheetah/README.md

Lines 86 to 88 in b9374ae

	```python
	segment.plot_overview(beam=beam)
	```