snap: Update snap summary.

Author: akashnimare

snap/snapcraft.yaml

@@ -1,7 +1,7 @@
 name: zulip
 version: 2.0.0
-summary: Zulip
-description: Zulip Desktop Client for Linux.
+summary: Zulip Desktop Client for Linux
+description: Zulip combines the immediacy of Slack with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones.
 confinement: strict
 grade: stable
 icon: snap/gui/icon.png