Comprehensively update user manual and contributor guide, add Adam to core team

website/content/learn/_unpublished/interface/layers-panel.md

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+title = "Layers panel"
+
+[extra]
+order = 3
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+
+This manual page hasn't been written yet! But here is an outline for what's coming soon:
+
+- About layers and folders
+- Control bar
+	- Blend modes and opacity
+	- Adding folders
+	- Deleting the selected layers
+- The layer list
+	- Editing layers
+	- Selection and multi-selection
+	- Rearranging the hierarchy

website/content/learn/_unpublished/interface/properties-panel.md

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+title = "Properties panel"
+
+[extra]
+order = 4
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+
+This manual page hasn't been written yet! But here is an outline for what's coming soon:
+
+- Node properties
+	- Parameters
+		- Expose button
+		- Name
+		- Value inputs