bugfix: Vertex should be replaced with a array<vec2f>

[hackaugusto]

Two small changes.

Wrong type on comment

@group(0) @binding(2) var<storage, read> pos: array<Vertex>;

could be replaced with:

@group(0) @binding(2) var<storage, read> pos: array<vec2f>;

instead of:

@group(0) @binding(2) var<storage, read> pos: vec2f;

Vertex was already define

The storage buffer article finishes with the shader code using the Vertex struct, the vertex buffer article started ignoring it. Changed the diff to show only the relevant changes while keeping continuity.

[greggman]

Sorry I missed this. Thanks!!!