Update code examples in docs (#18)

* Update README.md

* Update extract.go

* Update README.md

* Update README.md

* Update extract.go

Co-authored-by: Cristian Maglie <[email protected]>

Author: craig65535

README.md

@@ -9,13 +9,20 @@
 Package extract allows to extract archives in zip, tar.gz or tar.bz2 formats
 easily.
 
-Most of the time you'll just need to call the proper function with a buffer and
+Most of the time you'll just need to call the proper function with a Reader and
 a destination:
 
+```go
+file, _ := os.Open("path/to/file.tar.bz2")
+extract.Bz2(context.TODO, file, "/path/where/to/extract", nil)
+```
+
+or also:
+
 ```go
 data, _ := ioutil.ReadFile("path/to/file.tar.bz2")
 buffer := bytes.NewBuffer(data)
-extract.Bz2(context.Background(), buffer, "/path/where/to/extract", nil)
+extract.Bz2(context.TODO, buffer, "/path/where/to/extract", nil)
 ```
 
 Sometimes you'll want a bit more control over the files, such as extracting a
@@ -28,13 +35,13 @@ var shift = func(path string) string {
     parts = parts[1:]
     return strings.Join(parts, string(filepath.Separator))
 }
-extract.Bz2(data, "/path/where/to/extract", shift)
+extract.Bz2(context.TODO, file, "/path/where/to/extract", shift)
 ```
 
 If you don't know which archive you're dealing with (life really is always a surprise) you can use Archive, which will infer the type of archive from the first bytes
 
 ```go
-extract.Archive(data, "/path/where/to/extract", nil)
+extract.Archive(context.TODO, file, "/path/where/to/extract", nil)
 ```
 
 If you need more control over how your files will be extracted you can use an Extractor.
@@ -58,5 +65,5 @@ extractor := extract.Extractor{
     FS: fs,
 }
 
-extractor.Archive(data, "path/where/to/extract", nil)
+extractor.Archive(context.TODO, file, "/path/where/to/extract", nil)
 ```

extract.go

@@ -1,12 +1,11 @@
 // Package extract allows to extract archives in zip, tar.gz or tar.bz2 formats
 // easily.
 //
-// Most of the time you'll just need to call the proper function with a buffer and
+// Most of the time you'll just need to call the proper function with a Reader and
 // a destination:
 //
-// 	data, _ := ioutil.ReadFile("path/to/file.tar.bz2")
-// 	buffer := bytes.NewBuffer(data)
-// 	extract.TarBz2(data, "/path/where/to/extract", nil)
+// 	file, _ := os.Open("path/to/file.tar.bz2")
+// 	extract.Bz2(context.TODO, file, "/path/where/to/extract", nil)
 // ```
 //
 // Sometimes you'll want a bit more control over the files, such as extracting a
@@ -18,12 +17,12 @@
 //		parts = parts[1:]
 //		return strings.Join(parts, string(filepath.Separator))
 //	}
-//	extract.TarBz2(data, "/path/where/to/extract", shift)
+//	extract.Bz2(context.TODO, file, "/path/where/to/extract", shift)
 // ```
 //
 // If you don't know which archive you're dealing with (life really is always a surprise) you can use Archive, which will infer the type of archive from the first bytes
 //
-// 	extract.Archive(data, "/path/where/to/extract", nil)
+// 	extract.Archive(context.TODO, file, "/path/where/to/extract", nil)
 package extract
 
 import (