process(3lua): init man pages

Initialise man pages for the process module.

man/process/process.pidof.3lua.scd

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+PROCESS.PIDOF(3lua) "3lua" "Callisto manual pages"
+
+# NAME
+*process.pidof* - get the PID of another process
+
+# SYNOPSIS
+*process.pidof*(_cmd_: *string*)
+
+# DESCRIPTION
+*process.pidof* returns the PID of a process
+which has the command name _cmd_.
+The process is chosen arbitrarily; if there are multiple matches,
+the first process found with the command name _cmd_ is returned.
+
+If a process could not be found, *process.pidof* returns nil.
+
+# EXAMPLES
+Flawed implementation of *process.pid*:
+
+```
+function pid()
+	return process.pidof("csto")
+end
+```
+
+# SEE ALSO
+callisto(3lua), process(3lua)