The link_icons plugin prepends icon <img>s before registered link
types, like the link_css plugin adds class="..." attributes to the
html formatted links in every page.
prev << "linking/link_css"
next >> "linking/link_target_blank"

You cannot modify the README.plugins file, but anyhow any ideas or suggestion should as usually get filed on BugReports, UserSuggestions or even better the README.plugins.Discussion.