Documentation for git-pack-refs(1) --auto is incorrect

The documentation states:

   --auto
       Pack refs as needed depending on the current state of the ref database. The behavior depends on the ref format used by the repository and may
       change in the future.

       •   "files": No special handling for --auto has been implemented.

       •   "reftable": Tables are compacted such that they form a geometric sequence. For two tables N and N+1, where N+1 is newer, this maintains
           the property that N is at least twice as big as N+1. Only tables that violate this property are compacted.

However as of c3459ae9, this is no longer the case. We need to fix this.