Document that there can be multiple workers handling the receipts stream

[benbz]

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Noticed when inspecting #18581 that some of the documentation was changed to highlight that there can be multiple workers handling the receipts stream & I'm aware of instances running multipe receipts workers. Document this on workers.md too as this is the primary resource for worker configuration

[ll-SKY-ll]

"should be routed directly one of the workers"
looks like theres a "to" missing

[benbz]

Changed in ccedd56 along with the source that I copy/pasted from