add GPG example

Usage.md

@@ -0,0 +1,50 @@
+## Encryption with GPG
+
+_Replace `curl` with any other tool that can send HTTP POST requests. Example on Linux._ 
+
+ **Upload**
+
+String:
+: `echo "Cheers" | gpg --symmetric --armor | curl -X POST --data-binary @- https://linedump.com`
+
+File:
+: `gpg --symmetric --armor file.txt -o - | curl -X POST --data-binary @- https://linedump.com`
+
+Command:
+: `ip -br a | gpg --symmetric --armor | curl -X POST --data-binary @- https://linedump.com`
+
+ **Download**
+
+Save to file:
+: `curl -s https://linedump.com/{paste_id} | gpg --decrypt -o output.txt`
+
+### Example
+
+**1. Upload**
+
+```bash
+echo "Cheers" | gpg --symmetric --armor | curl -X POST --data-binary @- https://linedump.com
+https://linedump.com/xGuiMp
+Delete with HTTP POST: https://linedump.com/xGuiMp?token=x2NTpUh_JH7rwCdZ3gFDDAsCmAACkpYhZAaW0PP8
+```
+
+**2. Checking encrypted content the server sees**
+
+```bash
+curl https://linedump.com/xGuiMp
+-----BEGIN PGP MESSAGE-----
+
+jA0ECQMKjt5qCUrYoIj/0jwBPzikbS57PpJ0QR+5nlKXppAfkyVci7mI5kR3+zmC
+HOQYztfu4JXW1sEGaH3OPD0KlmBwpWIpbuSU2VE=
+=uRk1
+-----END PGP MESSAGE-----
+```
+
+**3. Download and decryption**
+
+```bash
+curl -s https://linedump.com/xGuiMp | gpg --decrypt
+gpg: AES256.CFB encrypted data
+gpg: encrypted with 1 passphrase
+Cheers
+```