Improve documentation of --psplash-pipe

[smcv]

• Correct parameter name when documenting --psplash-pipe in the man page
• Expand documentation of --psplash-pipe to specify what is reported

cc @agherzan

[dedekind]

Looks good to me. Simon, do you have push rights? If yes, I assume you can merge this yourself. If not, do you want the rights? If yes, I'll check how to give them to you, if not, I'll mere this one. Thanks!

[smcv]

I honestly don't know whether I can push. Let's find out!

[smcv]

Looks like I can :-)

[agherzan]

That looks good. Thanks @smcv