Add GC Support Staging Plan

Add implementation staging plan and status section to the GC-support documentation.

Documentation/llilc-gc.md

@@ -541,3 +541,22 @@ C++ methods or similar.
 
 A *PInvoke* (Platform Invoke) is a call to a native method from Jitted code.
 A *Reverse PInvoke* is a call to a Jitted method from native code.
+
+## Staging Plan
+
+No.  | Implementation | Testing | Issue | Status 
+---- |--------------- | --------| ------| -------  
+1 | Insert GC Safepoints: Run the PlaceSafepoints and RewriteSafepointsForGC phases before Code generation, and ensure that statepoints are inserted and lowered correctly | LLILC tests pass with Conservative GC | [32](https://github.com/dotnet/llilc/issues/32) | In Progress 
+2 |	Bring GCInfo library to LLILC: Use the GCInfo library to encode Function size correctly; no live pointers reported at GC-safe points | LLILC tests pass with Conservative GC  | [30](https://github.com/dotnet/llilc/issues/30) | In Progress
+3 | Report GC liveness: Encode GC pointer liveness information in the CLR format using the GC-Encoding library | A few functions compiled by LLILC with correct GCInfo, bail out on all other functions | [31](https://github.com/dotnet/llilc/issues/31) |
+4 | Test Pass |  LLILC tests pass with Precise GC, bail out on unimplemented features (see 7,8,9 below). Standard lab testing switched over to use Precise GC | | 
+5 | Add GC-specific stress tests| All existing and new tests pass | | 
+6 | GC Stress testing | Run the LLILC tests in GCStress mode; some GCStress testing running regularly in the lab | |
+7 | Special reporting for pinned pointers | Code with pinned pointers handled by LLILC | [29](https://github.com/dotnet/llilc/issues/29) | |
+8 | Support interior pointers | Code with interior pointers handled by LLILC | [33](https://github.com/dotnet/llilc/issues/33) | |
+9 | Fully-Interruptible code: Investigate whether fully interruptible code should be supported | Test and GCStress Pass | [473](https://github.com/dotnet/llilc/issues/473) | |
+10 | Lower Write barriers to Calls late | Test and GCStress Pass | [471](https://github.com/dotnet/llilc/issues/471) | | 
+11 | Place Safepoint-polls only where necessary for CoreCLR runtime | Test and GCStress Pass | [425](https://github.com/dotnet/llilc/issues/425) | |
+12 | Track GC-pointers in registers | Test and GCStress Pass | [474](https://github.com/dotnet/llilc/issues/474) | | 
+13 | Implement GC Checker | Test and GCStress Pass | [34](https://github.com/dotnet/llilc/issues/34) | |
+14 | Identify Object and Managed pointers differently| Test and GCStress Pass | [28](https://github.com/dotnet/llilc/issues/28) | |