chore: Update Lane Specific Readmes (backport #254)

[mergify]

This is an automatic backport of pull request #254 done by Mergify.
Cherry-pick of 4bfb7ce has failed:

On branch mergify/bp/release/v1.x.x/pr-254
Your branch is up to date with 'origin/release/v1.x.x'.

You are currently cherry-picking commit 4bfb7ce.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   block/proposals/proposals.go
	modified:   lanes/base/README.md
	modified:   lanes/free/README.md
	modified:   lanes/mev/README.md

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   abci/abci.go
	both modified:   block/proposals/proposals_test.go
	both modified:   lanes/base/abci_test.go
	both modified:   lanes/build-your-own/README.md
	both modified:   lanes/mev/abci_test.go
	both modified:   lanes/terminator/lane.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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