posixshmcontrol.1: Document posixshmcontrol create -l

[kib]

usr.bin/posixshmcontrol/posixshmcontrol.1

93

Is it clear that 'the page size' there refers to the page size specified for the option? (it is about the 'the' use, and I do not understand articles).

[markj]

usr.bin/posixshmcontrol/posixshmcontrol.1

93

It's not as clear as it could be. Possible interpretations would be "the system page size" or "the specified page size", so I changed it to the latter.

[markj]

Make it clear which page size we are talking about.