doc/gs/installation.texi: Added information how to install pcb on Fedora.

Signed-off-by: Bert Timmerman <bert.timmerman@xs4all.nl>
doc/gs/installation.texi: Added a remark about administrator-privileges.

Signed-off-by: Bert Timmerman <bert.timmerman@xs4all.nl>
doc/gs/installation.texi: better use "yum localinstall" to keep the updater synchronised.

Corrected some typos.

Signed-off-by: Bert Timmerman <bert.timmerman@xs4all.nl>