Added more property help docs

app/private/docs/property/damage-multiplier.md

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+# Damage multipliers
+
+Damage multipliers are used to define vulnerability, resistance, and immunity to damage types.
+
+A single multiplier can apply to multiple damage types, and choose whether or not to apply to an incoming source of damage based on the tags present on that damage.
+
+---
+
+### Name
+
+The name of the feature that gives this damage multiplier
+
+### Value
+
+- **Immunity** The creature takes no damage from matching damage sources
+- **Resistance** Damage from matching sources is halved.
+- **Vulnerability** Damage from matching sources is doubled.
+
+### Damage types
+
+A list of damage types that this property applies to. Custom types can be used.
+
+### Damage tags required
+
+This damage multiplier will only be applied if the incoming damage has all of these tags present.
+
+### Damage tags excluded
+
+This damage multiplier will only apply if the incoming damage has none of these tags present.
+
+### Tags
+
+See [Tags](/docs/tags)