switch_root, tailf, uuidparse, waitpid: add pages (#12108)

* switch_root, tailf, uuidparse, waitpid: add pages

---------

Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

pages/linux/waitpid.md

@@ -0,0 +1,25 @@
+# waitpid
+
+> Wait for the termination of arbitrary processes.
+> See also: `wait`.
+> More information: <https://manned.org/waitpid.1>.
+
+- Sleep until all processes whose PIDs have been specified have exited:
+
+`waitpid {{pid1 pid2 ...}}`
+
+- Sleep for at most `n` seconds:
+
+`waitpid --timeout {{n}} {{pid1 pid2 ...}}`
+
+- Do not error if specified PIDs have already exited:
+
+`waitpid --exited {{pid1 pid2 ...}}`
+
+- Sleep until `n` of the specified processes have exited:
+
+`waitpid --count {{n}} {{pid1 pid2 ...}}`
+
+- Display help:
+
+`waitpid -h`