Added changeset

Author: Izhak Lehmann

.changeset/five-islands-look.md

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+---
+"mobx": major
+---
+
+`computed`s are now kept alive by default (`keepAlive: true`)
+This changes unobserved computed behaviour - values stay cached instead being suspended or recomputed for each untracked read
+If you rely on previous behaviour, set "keepAlive: false" explicitly