Add readonly storage buffer example on render pipeline

[ottovilleFin]

Currently no WGSL samples covers this GLSL use case in vertex shader:

layout(std430, set = 0, binding = 0) readonly buffer myBuffer {
    float numbers[];
} myBuffer;

[austinEng]

Details of how readonly is specified is still in progress for WGSL. See https://github.com/gpuweb/gpuweb/issues/1159. Once that's finalized, I'll be happy to add an example that uses readonly storage buffers in the vertex shader :)

[caiiiycuk]

Hi, any updates on this?