Add Custom ClientStructs Docs

- Move RE to its own folder
- Add docs for using custom CS

docs/plugin-development/reverse-engineering/_category_.yml

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+label: Reverse Engineering
+position: 4
+link:
+  type: generated-index
+  title: Reverse Engineering
+  description: Learn how to reverse engineer the game.

docs/plugin-development/reverse-engineering/using-custom-cs.md

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+# Using Custom ClientStructs
+
+:::warning
+
+The Dalamud project discourages shipping custom versions of ClientStructs to end users. If you need a CS bump or have
+found a breakage in a specific version, please let the Dalamud maintainer team know!
+
+:::
+
+Oftentimes, ClientStructs contributors may want to verify or test their changes in a familiar codebase. Both Dalamud and
+ClientStructs provide the capability to do this, but some extra work needs to be done to get this working.
+
+### Prerequisites
+
+Using custom versions of Dalamud dependencies is not compatible with the provided `Dalamud.Plugin.targets` file. This
+will generally be the case if your plugin was based on [SamplePlugin](https://github.com/goatcorp/SamplePlugin), but
+may be there in other cases as well. You can check for this by looking for the below line in your `.csproj` file:
+
+```xml
+    <Import Project="$(DalamudLibPath)/targets/Dalamud.Plugin.targets"/>
+```
+
+If this is the case, you will need to delete this line and manually manage your dependencies. The easiest way to do this
+is to just copy the declarations from the [plugin targets file][plugin-targets] into your own `.csproj`. Please note
+that by doing this, your plugin will no longer automatically track the Dalamud-provided dependencies and Dalamud's 
+target framework. 
+
+You will also need to have successfully built ClientStructs at least once, and have the relevant artifacts ready to go.
+Developers who are actively working on ClientStructs should normally have this prerequisite met.
+
+[plugin-targets]: https://github.com/goatcorp/Dalamud/blob/master/targets/Dalamud.Plugin.targets
+
+### Building Against Custom Client Structs
+
+To use a custom ClientStructs, your plugin's `.csproj` file needs to be updated such that the `FFXIVClientStructs` 
+dependency is pointing to the resulting DLL. Depending on how your project is configured, this may take one of a few
+different methods, but will generally involve removing any `Reference`s mentioning `FFXIVClientStructs` and replacing it
+with something that looks similar to the one below:
+
+```xml
+    <Reference Include="FFXIVClientStructs">
+        <HintPath>C:\The\Path\To\Your\FFXIVClientStructs\bin\Debug\FFXIVClientStructs.dll</HintPath>
+        <Private>true</Private>  <!-- not necessary, but a good reminder -->
+    </Reference>
+```
+
+It is critical that the `Private` attribute either be set to `true` or unset. This will force MSBuild to copy the DLL
+to your plugin's output folder, which is in turn required to ensure that it's used over Dalamud's provided version.
+
+Once your `.csproj` is patched, you will additionally be responsible for [manually initializing the ClientStructs 
+resolver](https://github.com/aers/FFXIVClientStructs#signature-resolution). This is normally done by putting the
+following two lines of code in your plugin's constructor:
+
+```csharp
+FFXIVClientStructs.Interop.Resolver.GetInstance.SetupSearchSpace();
+FFXIVClientStructs.Interop.Resolver.GetInstance.Resolve();
+```
+
+While also not *strictly* necessary, it is generally good convention to run a `dotnet clean` on your project when
+switching to/from a custom ClientStructs build. This should be your first step in troubleshooting if things don't seem
+to be working properly.
+
+To revert these changes, simply undo your `.csproj` changes and remove the initializer code. It is generally advised to
+fall back to the Dalamud-provided ClientStructs when your testing is completed so that you don't inadvertently get stuck
+running a old forgotten DLL on your local computer.