Add shared directory README (dotnet/coreclr#10535)
Add shared directory README (dotnet/coreclr#10535)

* Add shared directory README

* PR feedback

Signed-off-by: dotnet-bot <03c4cb6107ae99956a7681f2c97ff7104809a2bd@microsoft.com>

tijoytom/corert,shrah/corert,yizhang82/corert,gregkalapos/corert,yizhang82/corert,botaberg/corert,shrah/corert,krytarowski/corert,krytarowski/corert,gregkalapos/corert,shrah/corert,botaberg/corert,krytarowski/corert,tijoytom/corert,krytarowski/corert,gregkalapos/corert,botaberg/corert,shrah/corert,yizhang82/corert,gregkalapos/corert,botaberg/corert,yizhang82/corert,tijoytom/corert,tijoytom/corert