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/goimports.md

@@ -7,7 +7,7 @@
 
 `goimports {{path/to/file}}.go`
 
-- Write the result back to the source file instead of the standard output:
+- Write the result back to the source file instead of `stdout`:
 
 `goimports -w {{path/to/file}}.go`