Change the zsh heading to unix.

unix/securely-remove-files.md

@@ -0,0 +1,11 @@
+# Securely Remove Files
+
+If you really want to make sure you have wiped a file from your hard drive,
+you are going to want to use `srm` instead of `rm`. The man page for `srm`
+gives the following description:
+
+> srm  removes  each  specified file by overwriting, renaming, and truncating
+> it before unlinking. This prevents other people from undeleting or
+> recovering any information about the file from the command line.
+
+h/t Dillon Hafer