Add snippet to generate certificates for minimal-server

Author: matzf

lib/shttp/examples/minimal/README.md

@@ -2,18 +2,23 @@ This example application makes two requests from the client to the server.
 
 First, it issues a GET request and downloads an HTML file. Afterwards it sends data to the server via POST.
 
-To run the example, first start the server like this
-```Go
-go run server.go -local 17-ffaa:1:c2,[127.0.0.1]:40002 -cert tls.pem -key tls.key
+To run the example, generate a certificate for the server first, e.g
+```sh
+openssl req -x509 -newkey rsa:1024 -keyout key.pem -nodes -out cert.pem -days 365 -subj '/CN=minimal-server'
+```
+
+Start the server like this
+```sh
+go run server.go -local 17-ffaa:1:c2,[127.0.0.1]:40002 -cert cert.pem -key key.pem
 ```
 
 Then, start the client:
-```Go
+```sh
 go run client.go -local 17-ffaa:1:c2,[127.0.0.1]:0
 ```
 
 For an interactive mode that lets the user choose a path from all available paths add the `-i` flag:
-```Go
+```sh
 go run client.go -local 17-ffaa:1:c2,[127.0.0.1]:0 -i
 ```
 
@@ -22,4 +27,4 @@ Make sure to replace the addresses with your own AS addresses and to set the TLS
 Also, `minimal-server` must resolve to the SCION address on which you run the server. You can add `minimal-server` to your known hosts by adding the following line to `/etc/hosts`. (replace `ISD-AS` and `IP` with your actual address):
 ```
 ISD-AS,[IP] minimal-server
-```
+```