docs: move lseek, sync and nice to the correct sections.
docs: move lseek, sync and nice to the correct sections.

* ext/posix/posix.c (lseek): Move to "File descriptors" section.
(sync): Move to "File system" section.
(nice): Move to "Process management" section.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

snegovick/luaposix,luaposix/luaposix,snegovick/luaposix,ardje/luaposix,ardje/luaposix,jimmyharris/luaposix,rrthomas/luaposix,zevv/luaposix,zevv/luaposix,rrthomas/luaposix,jimmyharris/luaposix