Updated readme to advise against pitching

Added bullet point to discourage people using the Slack to pitch their product or startup

README.md

@@ -3,6 +3,7 @@ Dated 1/18/17
 
 * Code for America has a code of conduct that applies to our spaces and events, including this the Code for America Slack channel.This [Code of Conduct can be found here.](https://github.com/codeforamerica/codeofconduct) 
 * Please be aware that Code for America staff may remove users _at will for any reason_ and _will_ remove any user that Code for America staff deems to be violating the Code for Conduct or are being disruptive. 
+* While Slack can be a great place to network, it should not be used to pitch companies or products without prompting. The expection to this is if people are looking for hire talent and are more than welcome to post in the #jobs-for-america channel.   
 * Please note that there are several government staff here in the Slack and any conversations posted in public channels may be subject to a Freedom of Information Act Request. Combined with the size of our Slack, users should treat the Code for America Slack the same way you would a message on a public forum. 
 * To keep pings down, the #announcements channel is admin-only channel. The @channel and @here commands have been disabled. 
 * Feel free to create channels, but keep in mind that Slack channels that are not active for three consecutive months will be archived.