Readme is misleading regarding releasable units

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#### Environment details
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#### Steps to reproduce
The steps in https://github.com/googleapis/release-please?tab=readme-ov-file#step-1-ensure-releasable-units-are-merged suggest that "deps" is a releasable unit. This is only true for some languages, but it is not the default.

As seen in https://github.com/googleapis/release-please/blob/main/src/util/filter-commits.ts#L20, the defaults are "feat", "fix", "perf", and "revert".