docs(en): write configuration pages

docs/en-US/configuration/ssh-keys.md

@@ -1 +1,25 @@
 # SSH key storage
+
+Along with configuration, termscp provides an essential feature for SFTP/SCP
+clients: the SSH key storage.
+
+To access the SSH key storage, enter the configuration and move to the
+`SSH Keys` tab.
+
+## Manage keys
+
+From the `SSH Keys` tab you can:
+
+- **Add a new key**: press `<CTRL+N>`. You are prompted to provide the
+  hostname/IP address and the username associated with the key, then a text
+  editor opens: paste the **private** SSH key into the editor, save and quit.
+- **Remove an existing key**: press `<DEL>` or `<CTRL+E>` on the key you want to
+  remove to delete it persistently from termscp.
+- **Edit an existing key**: press `<ENTER>` on the key you want to edit to change
+  the private key.
+
+## Password-protected keys
+
+Password-protected private keys are supported. The password you provide for
+authentication in termscp is valid both for username/password authentication and
+for key authentication.