2843 Update README for plugin list (cla: yes)

2847 [url_launcher_web] Add tel URL support (cla: yes)

2853 [connectivity] Endorse connectivity_for_web. (cla: yes)

2854 [e2e] Use SettableFutures instead of CompletableFuture (cla: yes)

2855 [e2e] Bump version to 0.6.0 (cla: yes)

2857 [url_launcher_linux] Add Linux url_launcher plugin (cla: yes)

2863 [url_launcher] Endorse url_launcher_linux (cla: yes)

2864 [shared_preferences] Shared preferences linux endorsement (cla: yes)

2865 [shared_preferences_linux] Add iOS stub (cla: yes)