added line for backing up moduli file

Author: k4yt3x

README.md

@@ -43,8 +43,12 @@ It's recommended to use the [ssh-audit](https://github.com/jtesta/ssh-audit) scr
 Diffie-Hellman moduli used for `diffie-hellman-group-exchange-sha256` should be at lest 3072 bits long according to [Mozilla's OpenSSH server hardening guide](https://infosec.mozilla.org/guidelines/openssh#modern-openssh-67). This can be done with the following commands.
 
 ```shell
+# backup original moduli file
+cp /etc/ssh/moduli /etc/ssh/moduli.backup
+
 # find lines with moduli >= 3071 bits and save them to moduli.tmp
 awk '$5 >= 3071' /etc/ssh/moduli > /etc/ssh/moduli.tmp
+
 # overwrite original moduli file with the updated one
 mv /etc/ssh/moduli.tmp /etc/ssh/moduli
 ```