add README

README.md

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+# unneko
+
+An extractor for Revived Witch nekodata.
+
+
+## Usage as binary 
+
+Download and run in terminal 
+
+```
+$ ./unneko -o ./output inputfile.nekodata
+```
+
+In case the inputfile is a patch nekodata the file extension must be `.patch.nekodata` 
+
+
+## Usage as library
+
+```go
+import "github.com/lico-n/unneko"
+
+func main() {
+  // initialize with nekodata filepath, if it's patch nekodata must contain `.patch.nekodata` file extension
+  r, err := unneko.NewReaderFromFile(inputFilePath)
+  handleError(err)
+
+  // alternatively initialize with in memory nekodata, must provide flag whether this is a patch file
+  var inMemoryNekoData []byte
+  isPatchFile := true 
+
+  r, err = unneko.NewReader(inMemoryNekoData, isPatchFile)
+  handleError(err)
+
+  // iterate over all extracted files
+  for r.HasNext() {
+    file, err := r.Next()
+    handleError(err)
+
+    file.Path() // original file path of the extracted file 
+    file.Data() // extracted data as byte array 
+  }
+
+}
+```
+
+