add "Update Zeppe-Lin" section

[sighook]

The documentation should describe about updating toolchain, libtool and other pitfalls of updating to new release.

[sighook]

Toolchain build order:

-> linux-api-headers (already included in glibc package)
 -> glibc{,32}
  -> binutils
   -> gcc
    -> libtool
     -> binutils (1)
      -> glibc (1)
       -> libtool (1)

NOTE: valgrind requires rebuilt with each major glibc version.