Add note about /bigobj and /Wa,-mbig-obj for Windows builds

Addresses hsutter#1227

Author: hsutter

docs/index.md

@@ -59,6 +59,8 @@ clang++ cppfront.cpp -std=c++20 -o cppfront
 
 That's it!
 
+> Note: On Windows (including MinGW), if you get a "too many sections" message, specify the switch `/bigobj` (MSVC) or `/Wa,-mbig-obj` (GCC).
+
 
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