perf inject: Clarify build-id options a little bit

perf inject: Clarify build-id options a little bit

Update the documentation of --build-id and --buildid-all options to
clarify the difference between them.  The former requires full sample
processing to find which DSOs are actually used.  While the latter simply
injects every DSO's build-id from MMAP{,2} records, skipping SAMPLEs.

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20220923173142.805896-3-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>