fix(readme): update how to specify custom build flags via CocoaPods (#20)

Author: craftzdog

README.md

@@ -299,7 +299,7 @@ post_install do |installer|
   installer.pods_project.targets.each do |target|
     if target.name == "react-native-quick-sqlite" then
       target.build_configurations.each do |config|
-        config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] ||= ['$(inherited)', '<SQLITE_FLAGS>']
+        config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] << 'SQLITE_ENABLE_FTS5=1'
       end
     end
   end