design-template: fix 'nick' spelling

'Nick' was spelled as 'Nic'.  Fix it and expand to 'Nickname' for
clarity.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I354c523e0bf2a2dcf9bb6d57cc246bec438ccb64
diff --git a/designs/design-template.md b/designs/design-template.md
index 120032e..858c128 100644
--- a/designs/design-template.md
+++ b/designs/design-template.md
@@ -28,13 +28,13 @@
 # Example design - this is the design title
 
 Author:
-  < Name and Discord nic >
+  < Name and Discord nickname >
 
 Primary assignee:
-  < Name and/or Discord nic or None >
+  < Name and/or Discord nickname or `None` >
 
 Other contributors:
-  < Name and/or Discord nic or None >
+  < Name and/or Discord nickname or `None` >
 
 Created:
   < Date initially created in Month D, Yr format (e.g. June 17, 2020 or Dec 19,