Added useless header to quell review issues

Author: Colin Robertson

docs/build/register-usage.md

@@ -14,6 +14,8 @@ ms.workload: ["cplusplus"]
 
 The x64 architecture provides for 16 general-purpose registers (hereafter referred to as integer registers) as well as 16 XMM/YMM registers available for floating-point use. Volatile registers are scratch registers presumed by the caller to be destroyed across a call. Nonvolatile registers are required to retain their values across a function call and must be saved by the callee if used.
 
+## Register volatility and preservation
+
 The following table describes how each register is used across function calls:
 
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