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/common/zcat.md

@@ -3,10 +3,10 @@
 > Print data from gzip compressed files.
 > More information: <https://www.gnu.org/software/gzip/manual/gzip.html>.
 
-- Print the uncompressed contents of a gzipped file to the standard output:
+- Print the uncompressed contents of a gzipped file to `stdout`:
 
 `zcat {{file.txt.gz}}`
 
-- Print compression details of a gzipped file to the standard output:
+- Print compression details of a gzipped file to `stdout`:
 
 `zcat -l {{file.txt.gz}}`