bug#23500: Manual:4.3 Guile Scripting: Show to a layman that Guile can invoke shell commands, which are common in bash scripts.

[Evan Davis]

In §4.3 (Guile Scripting) please mention §7.2.7 (Processes), or at
least the system/system* and open-pipe procedures.  Maybe include an
example of a guile script invoking shell commands, as is common in
bash.  As a layman, the manual's scripting section left me unsure
whether Guile could easily replace my typical bash scripts, and I
needed further help from Wingo on <irc://irc.freenode.net/guile>.