Update README with how to use subkeys example

README.md

@@ -120,6 +120,51 @@ jobs:
  git push
 ```
 
+### Use a subkey
+
+With the input `fingerprint`, you can specify which one of the subkeys in a GPG key you want to use for signing.
+
+```yaml
+name: import-gpg
+
+on:
+ push:
+ branches: master
+
+jobs:
+ import-gpg:
+ runs-on: ubuntu-latest
+ steps:
+ -
+ name: Checkout
+ uses: actions/checkout@v2
+ -
+ name: Import GPG key
+ id: import_gpg
+ uses: crazy-max/ghaction-import-gpg@v4
+ with:
+ gpg_private_key: ${{ secrets.GPG_PRIVATE_KEY }}
+ passphrase: ${{ secrets.PASSPHRASE }}
+ fingerprint: "C17D11ADF199F12A30A0910F1F80449BE0B08CB8"
+ -
+ name: List keys
+ run: gpg -K
+```
+
+For example, given this GPG key with a signing subkey:
+
+```s
+pub ed25519 2021-09-24 [C]
+ 87F257B89CE462100BEC0FFE6071D218380FDCC8
+ Keygrip = F5C3ABFAAB36B427FD98C4EDD0387E08EA1E8092
+uid [ unknown] Joe Bar <[email protected]>
+sub ed25519 2021-09-24 [S]
+ C17D11ADF199F12A30A0910F1F80449BE0B08CB8
+ Keygrip = DEE0FC98F441519CA5DE5D79773CB29009695FEB
+```
+
+You can use the subkey with signing capability whose fingerprint is `C17D11ADF199F12A30A0910F1F80449BE0B08CB8`.
+
 ## Customizing
 
 ### inputs