feat: add model upgrades page (#385)

Co-authored-by: glihm <[email protected]>

docs/pages/framework/models/upgrades.md

@@ -0,0 +1,53 @@
+---
+title: Upgrades models in Dojo
+description: Learn how to upgrade models in Dojo.
+---
+
+# Upgrades
+
+In Dojo, all models are upgradeable, which means that when their code changes, they are redeployed 
+to the same address, preserving the existing model storage and therefore the existing model data.
+
+However, to be able to preserve existing model data, there are some limitations.
+
+## General rules
+
+- To be upgradeable, the layout of a model must not be packed (using `IntrospectPacked`).
+
+- For composite data structures like `struct`, `enum`, `tuple` and `array`
+    - they are upgreadable as soon as all their elements are upgreadable,
+    - existing elements cannot be removed, they can only be modified according to the rules described 
+  on this page. New elements can be freely added.
+
+- Each element of a data structure must keep the same type (i.e a `tuple` must remain a `tuple`), the same name and
+  the same attributes if any (such as `#[key]` for model members).
+
+- A primitive type can be upgraded to a larger primitive type as soon as its felt252 representation uses the same number of felts
+(for example, `u8` to `u128` but not `u128` to `u256`). See the next chapter for more details.
+
+- A key model member is upgradeable only if its type is an upgreadable primitive or an enum with new variants only (existing variants cannot be
+modified for a key member).
+
+## Primitive upgrades
+
+This table lists the allowed upgrades for every primitive types.
+The type `usize` is not supported since it is a architecture-dependent type.
+
+| Current         | Allowed upgrades |
+| --------------- | ---------------- |
+| bool            | bool, felt252 |
+| u8              | u8 to u128, felt252 |
+| u16             | u16 to u128, felt252 |
+| u32             | u32 to u128, felt252 |
+| u64             | u64 and u128, felt252 |
+| u128            | u128, felt252 |
+| u256            | u256 |
+| i8              | i8 to i128, felt252 |
+| i16             | i16 to i128, felt252 |
+| i32             | i32 to i128, felt252 |
+| i64             | i64 and i128, felt252 |
+| i128            | i128, felt252 |
+| felt252         | felt252, ClassHash, ContractAddress |
+| ClassHash       | felt252, ClassHash, ContractAddress |
+| ContractAddress | felt252, ClassHash, ContractAddress |
+| EthAddress      | felt252, ClassHash, ContractAddress, EthAddress |

routes.ts

@@ -75,6 +75,7 @@ export const routes = [
                     },
                     { text: "Entities", link: "/framework/models/entities" },
                     { text: "Enum", link: "/framework/models/enum" },
+                    { text: "Upgrades", link: "/framework/models/upgrades" },
                 ],
             },
             {