Assembly - add airspeed sensor

[hamishwillee]

Adds airspeed sensor to the assembly guide, displayed for VTOL/FW only.

Since these sensors are I2C usually, I also updated I2C page to include info about I2C splitters and level converters, since you need those in some cases.

I updated the basic concepts to also mention other sensors such as airspeed, optical flow and distance sensors since these are "more important".

I have not yet added info on distance sensors to assembly. Unlike airspeed sensors they use all kinds of busses, so not sure yet the right way to approach this.

FYI @sfuhrer

[github-actions[bot]]

No flaws found

[sfuhrer]

Nice!