Update README.md: add command to export GPG key

README.md

@@ -37,6 +37,17 @@ To import a gpg key, use `gpg --import <key file>`. To import all keys, go to GP
 After that, you need to edit confidence of the key. For this, use `gpg --edit-key <keyName>` and use `trust` command in gpg (`gpg>trust`)
 Answer the response to add the confidence `5 - ultimate`. Use `quit` to leave.
 
+## Export the key
+Find the ID of your key, for example with
+```sh
+gpg --list-keys | grep -i -B 2 <your name>
+```
+Then export it
+```sh
+gpg --export --armor --output '<your.email@tetras-libre.fr_pub.asc' <key id>
+```
+Finally copy the `.asc` key file to the GPG folder (if it's not already there)
+
 
 # Pass
 ## Check manually if key is valid for pass