man tpm2_getrandom: add missing --hex parameter in example

The example demonstrating hex output was missing the --hex flag,
which would cause the command to output binary data instead of
the intended hexadecimal format.

Signed-off-by: Zhirang Guo <jonny_guo@apple.com>

Author: Zhirang Guo

man/tpm2_getrandom.1.md

@@ -76,7 +76,7 @@ tpm2_getrandom -o random.out 20
 
 ## Generate a random 8 bytes and output the hex formatted data to stdout
 ```bash
-tpm2_getrandom 8
+tpm2_getrandom 8 --hex
 ```
 
 [returns](common/returns.md)