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/osx/wc.md

@@ -19,6 +19,6 @@
 
 `wc -m {{path/to/file}}`
 
-- Use standard input to count lines, words and characters (bytes) in that order:
+- Use `stdin` to count lines, words and characters (bytes) in that order:
 
 `{{find .}} | wc`