Add viscosity role for macOS

macOS.yaml

@@ -8,3 +8,4 @@
     - role: iterm
     - role: magnet
     - role: obsidian
+    - role: viscosity

roles/viscosity/tasks/main.yaml

@@ -0,0 +1,8 @@
+---
+- assert:
+    that: ansible_os_family == "Darwin"
+
+- name: install homebrew package
+  homebrew_cask:
+    name: viscosity
+    state: latest