`AxisTensor`s have no documentation

Searching axistensors in the docs

Searching in the code base gives a little more
```julia
"""
AxisTensor(axes, components)

An `AxisTensor` is a wrapper around a `StaticArray`, where each dimension is
labelled with an [`AbstractAxis`](@ref). These axes must be consistent for
operations such as addition or subtraction, or be dual to each other for
operations such as multiplication.

# See also
[`components`](@ref) to obtain the underlying array.
"""
```

this is not enough to understand what they are for and how to use them

Start by searching the documentation and codebase for `AxisTensor` and reviewing its existing docstring. Document what `AxisTensor`s are for and how to use them, including enough context beyond the current definition to make the concept understandable; the issue is complete when users can find and follow practical guidance in the docs.

Written by the indexing model from the issue text.