Adapt information about Tramp's temporary directory

Adapt information about Tramp's temporary directory

* doc/misc/tramp.texi (Overview): Use scp in the example.
(FUSE-based methods): Move information about mount point to node
"FUSE setup".
(Overview, Predefined connection information, FUSE setup)
(Traces and Profiles): Refer to node "Temporary directory".
(Frequently Asked Questions): Move information about temporary
directory to node "Temporary directory".
(Temporary directory): New node.
(Top, Files directories and localnames): Add it to @menu.