Document f16c target feature

src/attributes/codegen.md

@@ -89,6 +89,7 @@ Feature     | Implicitly Enables | Description
 `bmi1`      |          | [BMI1] — Bit Manipulation Instruction Sets
 `bmi2`      |          | [BMI2] — Bit Manipulation Instruction Sets 2
 `cmpxchg16b`|          | [`cmpxchg16b`] - Compares and exchange 16 bytes (128 bits) of data atomically
+`f16c`      | `avx`    | [F16C] — 16-bit floating point conversion instructions
 `fma`       | `avx`    | [FMA3] — Three-operand fused multiply-add
 `fxsr`      |          | [`fxsave`] and [`fxrstor`] — Save and restore x87 FPU, MMX Technology, and SSE State
 `lzcnt`     |          | [`lzcnt`] — Leading zeros count
@@ -117,6 +118,7 @@ Feature     | Implicitly Enables | Description
 [BMI1]: https://en.wikipedia.org/wiki/Bit_Manipulation_Instruction_Sets
 [BMI2]: https://en.wikipedia.org/wiki/Bit_Manipulation_Instruction_Sets#BMI2
 [`cmpxchg16b`]: https://www.felixcloutier.com/x86/cmpxchg8b:cmpxchg16b
+[F16C]: https://en.wikipedia.org/wiki/F16C
 [FMA3]: https://en.wikipedia.org/wiki/FMA_instruction_set
 [`fxsave`]: https://www.felixcloutier.com/x86/fxsave
 [`fxrstor`]: https://www.felixcloutier.com/x86/fxrstor