pages/*: add backticks around I/O streams (#10436)

* as suggested in #10428
* standard input  => `stdin`
* standard output => `stdout`
* standard error  => `stderr`

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/linux/logsave.md

@@ -7,7 +7,7 @@
 
 `logsave {{path/to/logfile}} {{command}}`
 
-- Take input from standard input and save it in a log file:
+- Take input from `stdin` and save it in a log file:
 
 `logsave {{logfile}} -`