Merge pull request #195 from hoonv/update-readme

Update SPM Installation more detail

Author: lucdion

README.md

@@ -1111,7 +1111,7 @@ To integrate FlexLayout into another Swift Package, add it as a dependency:
 #### In an Xcode target
 
 1. To integrate FlexLayout into an Xcode target, use the `File -> Swift Packages -> Add Package Dependency` menu item.
-2. Add "FLEXLAYOUT_SWIFT_PACKAGE=1" to the Xcode target's `GCC_PREPROCESSOR_DEFINITIONS` build setting.
+2. Add "FLEXLAYOUT_SWIFT_PACKAGE=1" to the Xcode target's `GCC_PREPROCESSOR_DEFINITIONS` build setting. (TARGET -> Build Settings -> Apple Clang-Preprocessing -> Preprocessor Macros)
 
 
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