pldd.1: Minor wording fixes

pldd.1: Minor wording fixes

* Establish the abbreviations DSO and PID in the lead paragraph
  since they are used later.
* Parallelize descriptions of help, usage, and version options
  with the "and exit" language used in getent(1), iconv(1),
  locale(1), localedef(1), memusage(1), memusagestat(1),
  mtrace(1), pldd(1), sprof(1), time(1), iconvconfig(8),
  zdump(8), and zic(8).

Signed-off-by: G. Branden Robinson <g.branden.robinson@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>