mention higher arch requirement for amd64 race detector

It needs SSE3, which is not required by the base amd64 configuation.

Fixes golang/go#68251

Change-Id: I9b680b35d92adc6c9fdc41945746cd0c44309681
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/595976
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: randall77

MinimumRequirements.md

@@ -92,6 +92,8 @@ The Go toolchain may also generate newer instructions, but guarded by dynamic ch
 
 The Go toolchain does not currently generate any AVX512 instructions.
 
+The race detector is not supported on platforms that do not provide SSE3.
+
 Note that *processor* is a simplification in this context. In practice, support from the entire system (firmware, hypervisor, kernel) is needed.
 
 See section [Microarchitecture support](#microarchitecture-support) for hints on how to use microarchitecture environment variables like GOAMD64.