Improve documentation - add notice about public key

documentation/v0.2.0/getting-started.md

@@ -246,6 +246,18 @@ $ ssh-keygen -p -f <filename> -m pem
 
 Then copy content from generated file. 
 
+#### Public key
+
+If you want to upload your public key to your Git server you need to extract it.
+
+If key was generated by `openssl` then you need to type this to extract public key:
+
+```bash
+$ openssl rsa -in <filename> -pubout > <filename>.pub
+```
+
+If key was generated by `ssh-keygen` the public key content is located in <filename>.pub and there is no need to extract public key
+
 #### Configure SSH authentication
 
 Configure seed job like: