Change to base64-URL encoding and remove xdg-open

URL version of base64 encoding should be used instead, therefore appropriate conversion is applied in the command. Further, `xdg-open` isn't cross-platform, so it was removed.

lnd_connect_uri.md

@@ -35,7 +35,7 @@ var url = 'lndconnect://' + ip.address() + ':10009?cert=' + cert + '&macaroon='
 This is useful when one doesn't want to bring dependencies.
 
 ```
-echo 'lndconnect://example.com?cert='"`grep -v 'CERTIFICATE' tls.cert`"'&macaroon='"`base64 admin.macaroon`" | tr -d '\n' | qrencode -o /tmp/out.png && xdg-open /tmp/out.png
+echo 'lndconnect://example.com?cert='"`grep -v 'CERTIFICATE' tls.cert | tr -d '=' | tr '/+' '_-'`"'&macaroon='"`base64 admin.macaroon | tr -d '=' | tr '/+' '_-'`" | tr -d '\n' | qrencode -o /tmp/out.png
 ```
 
 ## Example: