separate npmignore entries into their related folders

.npmignore

@@ -1,52 +1,2 @@
-node_modules/
-.idea/
-Example/
-experimental/
-android/build/
 screenshots/
 idl/
-flow-typed/
-
-# OSX
-#
-.DS_Store
-
-# Xcode
-#
-*.pbxuser
-!default.pbxuser
-*.mode1v3
-!default.mode1v3
-*.mode2v3
-!default.mode2v3
-*.perspectivev3
-!default.perspectivev3
-xcuserdata
-*.xccheckout
-*.moved-aside
-DerivedData
-*.hmap
-*.ipa
-gradle
-project.xcworkspace
-
-# Android/IJ
-#
-.idea
-.gradle
-local.properties
-build
-
-# node.js
-#
-node_modules
-npm-debug.log
-
-
-# webstorm
-#
-*.iml
-
-# unfinished documents
-#
-cn-doc.md