Add https://github.com/dnsimple/dnsimple-csharp examples

I followed your instructions for creating a user token in the web interface.
I placed that token in token.rb as directed.
When I run ./zone_records.rb example.com, it throws an exception because account in the response object is nil.

#<Dnsimple::Response:0x007fa4862d6630
@DaTa=
#<Dnsimple::Struct::Whoami:0x007fa4862d6900
@account=nil,
@user=
#<Dnsimple::Struct::User:0x007fa4862d6838
@email="[email protected]",
@id=12345>>,
@http_response=
{"data"=>
{"user"=>
{"id"=>12345,
"email"=>"[email protected]",
"created_at"=>"2016-01-15T12:15:36.956Z",
"updated_at"=>"2016-11-16T11:13:15.498Z"},
"account"=>nil}},
@rate_limit=2400,
@rate_limit_remaining=2399,
@rate_limit_reset=2016-11-18 08:47:13 -0500>