docs: provide co-author guidance in contributer guide. (#11381)
docs: provide co-author guidance in contributer guide. (#11381)

Addresses
https://github.com/envoyproxy/envoy/pull/11007#issuecomment-635009257.

Signed-off-by: Harvey Tuch <c185081708e02336640916420d0c772668570de5@google.com>
lizan/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,lizan/envoy,lyft/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy-wasm,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,lyft/envoy,lyft/envoy,envoyproxy/envoy,lizan/envoy,lizan/envoy,lyft/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy-wasm,lyft/envoy