Add missing example

[eschnett]

No description provided.

[chakravala]

An example is already given a few lines above that
https://github.com/chakravala/DirectSum.jl/blame/c72c52cdfa3e46a9565a53aee2c06e82db407609/README.md#L158

It may have been easy to miss because it is on the same line as using statement.

julia> using DirectSum; @basis ℝ^3 # equivalent to basis"+++"
(⟨+++⟩, v, v₁, v₂, v₃, v₁₂, v₁₃, v₂₃, v₁₂₃)

I don't want the same example twice, but perhaps, instead of adding a second example, the original one should be moved to a new line to make it more clear.

[eschnett]

The missing example is for the syntax to give custom names to the vector space and basis vectors (S, b). This is mentioned in the first half of the preceding paragraph. Instead of having both examples together, the paragraph could be split into two, and the example in between the two halves.

[chakravala]

Aha, well the README is not supposed to be a comprehensive manual, which is why I intentionally truncated it from what's in the documentation website. It's only supposed to give some teasers and a general impression, while documuntation website is supposed to contain what will eventually be the full manual.

If you would like to add more details for a more complete manual, it would be better to submit it to the documentation web page instead of the README.

[eschnett]

That's fine. However, since the paragraph above my new example explicitly says:

"In the following command, the @basis macro arguments are used to assign the vector space name to S instead of V and basis elements to b instead of v, so that their local names do not interfere."

... I thought that the following command should actually do that.

[chakravala]

Good point. At the moment I'm unsure, but maybe that sentence needs to be deleted.