Add GPG YubiKey switch helper script

gpg-switch-yubikey/README.md

@@ -0,0 +1,26 @@
+# gpg-switch-yubikey
+
+Switch GPG between two YubiKeys that hold identical key material.
+
+GPG binds secret key stubs to a specific card serial number. When you swap YubiKeys, GPG prompts you to insert the other one. This script deletes the stubs and re-learns whichever card is currently inserted.
+
+## Install
+
+```bash
+cp gpg-switch-yubikey ~/.local/bin/
+chmod +x ~/.local/bin/gpg-switch-yubikey
+```
+
+Make sure `~/.local/bin` is in your `PATH`.
+
+## Usage
+
+After physically swapping to a different YubiKey:
+
+```bash
+gpg-switch-yubikey
+```
+
+## Configuration
+
+The script contains a hardcoded GPG key fingerprint. Edit the `FINGERPRINT` variable in the script to match your own key.