secret-tool (libsecret): add page

Add page documenting simple commands to store and lookup secrets from
libsecret.

pages/linux/secret-tool.md

@@ -0,0 +1,22 @@
+# secret-tool
+
+> Store and retrieve passwords, part of the `libsecret` package.
+> Communicates with `Secret Service` implementation such as `gnome-keyring`.
+> For more information <https://wiki.gnome.org/Projects/Libsecret>.
+
+- Store a secret with optional label:
+
+`secret-tool store --label={{label}} {{key}} {{value}}`
+
+- Retrieve a secret:
+
+`secret-tool lookup key {{key}}`
+
+- Get more information about secret:
+
+`secret-tool search key {{key}}`
+
+- Delete a stored secret:
+
+`secret-tool clear key {{key}}`
+