Change "translator_credits-PLEASE_ADD_YOURSELF_HERE" to "translator-credits"
In the po file i translate i see:
I guess it should just be this which other software seem to use:
And write any comment for translations with lines starting with "#." instead og inside msgid.
Example from gnome-tetravex:
#. Translators: about dialog text; this string should be replaced by a text crediting yourselves and your translation team, or should be left empty. Do not translate literally! msgid "translator-credits"