docs(dependency-set): specify that dependency is bidirectional

[qbzzt]

Description

Change the specs to match what I heard from @zainbacchus in our call today (unless I misunderstood).

Tests

N/A

Additional context

N/A

Metadata

N/A

[tynes]

I think this needs a bit more explaining, specifically around why and how. Perhaps this information isn't super legible, its part of #465

[zainbacchus]

This should be helpful: ethereum-optimism/docs#1171

[zainbacchus]

Closing this as this change was reverted. See:ethereum-optimism/docs#1186

[qbzzt]

I don't understand. Can chainA be in the dependency set of chainB if chainB is not in the dependency set of chainA? In other words, is it possible for me to send an interop message A->B, but not B->A? If so then the change I proposed is wrong. If not, it is necessary for accuracy.

Changing the docs should not affect the specs, IMAO.