Add instructions for building with reflection.

P2996.md

@@ -13,6 +13,7 @@ The intent of this project is to continue tracking changes to P2996 as it makes
 
 - [Rationale](#rationale)
 - [Acknowledgments](#acknowledgments)
+- [Quick start](#quick-start)
 - [Implementation status](#implementation-status)
   - [Incomplete features](#incomplete-features)
   - [P2996 test cases](#p2996-test-cases)
@@ -37,6 +38,10 @@ This project owes an enormous debt to the historical [paper/p2320](https://githu
 The initial implementation of Clang/P2996 was led by Dan Katz, with significant contributions from Georgi Koyrushki, Mark Sciabica, Sergei Murzin, and Kay Hicketts. All are engineers at Bloomberg, and they are grateful to their organization for supporting this work.
 
 
+## Quick start
+The upstream LLVM project provides an excellent [Getting Started](https://llvm.org/docs/GettingStarted.html) guide with instructions for building `clang` and `libc++`. After building both of these targets, support for reflection can be enabled in Clang/P2996 by compiling with both the `-std=c++26` and `-freflection` flags.
+
+
 ## Implementation status
 At present, Clang/P2996 supports: