stub out guide

Author: runspired

guides/reactive-data/legacy/overview.md

@@ -4,3 +4,12 @@
 
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+🚧 This guide is under active construction, it will talk about the below points 🚧 
+
+In LegacyMode records are:
+
+- mutable
+- local changes immediately reflect app wide
+- all the APIs of Model (references, state props, currentState, methods etc)
+- limited reactivity for fields (same as Model)
+- requires continued use of the `model` and `legacy-compat` packages (though most imports from them can be removed)

guides/reactive-data/polaris/overview.md

@@ -4,3 +4,14 @@
 
 ---
 
+🚧 This guide is under active construction, it will talk about the below points 🚧 
+
+In PolarisMode records are:
+
+- immutable (unless creating or checking out for editing)
+- local changes only show where you want them to on the editable version
+- none of the APIs of Model (references, state props, currentState, methods etc)
+- deep reactivity for fields
+- advanced derivations, aliasing and transformations
+- [currently] limited support for relationships
+- no promise proxies for relationships