Add dev day disruption

Author: hsnfirooz

help/garage.rst

@@ -6,6 +6,10 @@ Scicomp garage
 
    https://aalto.zoom.us/j/61322268370, every workday at 13:00
 
+.. admonition:: Planned disruptions
+   :class: important
+
+   * September 30: We do have an internal development day. There is no garage session.
 
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 be.  It's not just Triton, but all aspects of scientific computing.