Please, don't start a conversation in a messenger with a single "hello" message without anything else. If you do, you make the receiver wait. This leads to frustration and wasted time on their end. Instead, put your question or request right in your first message!
Also, please, don't ask permission to ask. Those "Do you have a moment?" or "May I ask you a question?" do not add anything to the conversation. You may be trying to be polite but in fact you turn an asynchronous communication into a synchonous one. Respect the time of the person you are writing to.
Share this link in "general" channel in your slack and set it as a status. Help making the world a better place!