Add some docs around spam (#207)

Author: DLeyland

knowledge-base/kb-prevent-spam.mdx

@@ -0,0 +1,10 @@
+---
+title: How do I prevent spam emails from being sent to my team?
+---
+
+If you consistently receive spam emails from the same source, you can mark that customer as spam in order to not see their emails in Plain.
+
+If this doesn't help then get in touch with us and we can configure custom spam filtering for you.
+
+
+

knowledge-base/kb-unmark-spam.mdx

@@ -0,0 +1,10 @@
+---
+title: How do I unmark a customer as spam?
+---
+
+When you mark a customer as spam you will no longer see their threads in the queue in Plain and they will not be included in reporting. 
+
+You can see a list of all the customers you've marked as spam on the spam settings page at `Settings > Spam`.
+
+To unmark a customer as spam, simply click the `Unmark as spam` button next to their name.
+

knowledge-base/overview.mdx

@@ -15,3 +15,7 @@ sidebarTitle: Overview
 
 ### Security
 - [Are you SOC2 certified?](./kb-soc2)
+
+### Spam
+- [How do I prevent spam emails from being sent to my team?](./kb-prevent-spam)
+- [How do I unmark a customer as spam?](./kb-unmark-spam)