unshadow: add page (#4041)

Co-authored-by: Starbeamrainbowlabs <sbrl@starbeamrainbowlabs.com>

pages/linux/unshadow.md

@@ -0,0 +1,12 @@
+# unshadow
+
+> Utility provided by the John the Ripper project to obtain the traditional Unix password file if the system uses shadow passwords.
+> More information: <https://www.openwall.com/john/>.
+
+- Combine the /etc/shadow and /etc/passwd of the current system:
+
+`sudo unshadow /etc/passwd /etc/shadow`
+
+- Combine two arbitrary shadow and password files:
+
+`sudo unshadow {{/path/to/passwd}} {{/path/to/shadow}}`