[libpng16] Expand INSTALL instructions about enabling hardware optimizations.
diff --git a/INSTALL b/INSTALL
index 5a957a6..c527938 100644
--- a/INSTALL
+++ b/INSTALL
@@ -285,7 +285,22 @@
XIV. Enabling or disabling hardware optimizations
Certain hardware capabilites, such as the Intel SSE instructions,
-are normally detected at run time. If you wish to avoid using them,
+are normally detected at run time. Enable them with configure options
+such as one of
+
+ --enable-arm-neon=yes
+ --enable-mips-msa=yes
+ --enable-intel-sse=yes
+ --enable-powerpc-vsx=yes
+
+or, if you are not using "configure", you can use one of
+
+ CPPFLAGS += "-DPNG_ARM_NEON"
+ CPPFLAGS += "-DPNG_MIPS_MSA"
+ CPPFLAGS += "-DPNG_INTEL_SSE"
+ CPPFLAGS += "-DPNG_POWERPC_VSX"
+
+If you wish to avoid using them,
you can disable them via configure options such as
--enable-arm-neon=no, --enable-mips-msa=no, --enable-intel-sse=no,
