following to change notation on #3929

Author: vorj

INSTALL.md

@@ -131,7 +131,7 @@ Several options can be passed to CMake, among which:
   optimization options (enables `-O3` on gcc for instance),
   - `-DFAISS_OPT_LEVEL=avx2` in order to enable the required compiler flags to
   generate code using optimized SIMD/Vector instructions. Possible values are below:
-    - On x86\_64, `generic`, `avx2` and `avx512`, by increasing order of optimization,
+    - On x86-64, `generic`, `avx2` and `avx512`, by increasing order of optimization,
     - On aarch64, `generic` and `sve`, by increasing order of optimization,
   - `-DFAISS_USE_LTO=ON` in order to enable [Link-Time Optimization](https://en.wikipedia.org/wiki/Link-time_optimization) (default is `OFF`, possible values are `ON` and `OFF`).
 - BLAS-related options: