Update readme

README.md

@@ -1 +1,102 @@
-# treefs
+Package treefs provides functionality to print a simple graph of an fs.FS using
+the template of the [`tree` command](https://en.wikipedia.org/wiki/Tree_(command)).
+
+The version of `tree` whose graph is mimicked is tree v2.0.2 (c) 1996 - 2022 by
+Steve Baker, Thomas Moore, Francesc Rocher, Florian Sesser, Kyosuke Tokoro.
+
+To get the graph representation and metadata of an fs.FS, construct a TreeFS
+and use its String method.
+
+Consider the following directory (whose graph was generated by tree v2.0.2)
+
+    testdata
+    └── a
+        ├── a1.test
+        ├── a2.test
+        ├── a3.test
+        ├── b
+        │   ├── b1.test
+        │   ├── b2.test
+        │   ├── b3.test
+        │   └── d
+        │       └── d1.test
+        └── c
+            ├── c1.test
+            └── c2.test
+
+    4 directories, 9 files
+
+Its graph could be constructed using treefs in the following way
+
+```go
+	var testdataFS fs.FS // assume this is embeded or read with os.DirFS
+	tfs, err := New(testdataFS, "testdata")
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(tfs)
+```
+
+which would generate the following output
+
+    testdata
+    └── a
+        ├── a1.test
+        ├── a2.test
+        ├── a3.test
+        ├── b
+        │   ├── b1.test
+        │   ├── b2.test
+        │   ├── b3.test
+        │   └── d
+        │       └── d1.test
+        └── c
+            ├── c1.test
+            └── c2.test
+
+    4 directories, 9 files
+
+Aggregated trees are allowed as well:
+
+```go
+	var args []Arg // see internal/examples/multi
+	multitfs, err := NewMutli(args...)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(multitfs)
+```
+
+could result in the following aggregate
+
+    .
+    └── main.go
+    ../../../../treefs
+    ├── LICENSE
+    ├── go.mod
+    ├── internal
+    │   └── examples
+    │       ├── multi
+    │       │   └── main.go
+    │       └── single
+    │           └── main.go
+    ├── testdata
+    │   └── a
+    │       ├── a1.test
+    │       ├── a2.test
+    │       ├── a3.test
+    │       ├── b
+    │       │   ├── b1.test
+    │       │   ├── b2.test
+    │       │   ├── b3.test
+    │       │   └── d
+    │       │       └── d1.test
+    │       └── c
+    │           ├── c1.test
+    │           └── c2.test
+    ├── treefs.go
+    └── treefs_test.go
+
+    9 directories, 16 files
+
+See [`internal/examples`](https://github.com/Algebra8/treefs/tree/main/internal/examples) for example usage.