readme: several updates

- replace the old low-level video with the new high-level one, and place
  it with screenshot prominently at the top

- increase default ccache size

- remove obsolete NOTEs

- add blurb about patching modules and -t

- "trampoline" -> "handler"

- more details about ftrace, perf, tracepoints compatibility

- add recommended practice re: single cumulative module vs multiple
  independent modules