Update the readme.

Author: schmidtw

README.md

@@ -6,4 +6,65 @@
 [![GitHub Release](https://img.shields.io/github/release/schmidtw/githubfs.svg)](CHANGELOG.md)
 [![GoDoc](https://pkg.go.dev/badge/github.com/schmidtw/githubfs)](https://pkg.go.dev/github.com/schmidtw/githubfs)
 
-A go fs.FS based github filesystem.
+A simple to use go fs.FS based github filesystem.
+
+## Resulting Directory Structure
+
+```
+org_or_user/                    // org or username
+└── repository                  // repository
+    ├── git                     // fixed name 'git'
+    │   └── main                // the branch name
+    │       └── README.md       // the files in the repo
+    └── releases                // fixed name 'releases'
+        └── v0.0.1              // release version
+            └── description.md  // the description of the release and other files from the release
+```
+
+## Example Usage
+
+```golang
+package githubfs
+
+import (
+	"context"
+	"fmt"
+	"io/fs"
+	"os"
+
+	"github.com/schmidtw/githubfs"
+	"golang.org/x/oauth2"
+)
+
+func main() {
+	src := oauth2.StaticTokenSource(
+		&oauth2.Token{AccessToken: os.Getenv("GITHUB_TOKEN")},
+	)
+	httpClient := oauth2.NewClient(context.Background(), src)
+
+	gfs := githubfs.New(
+		githubfs.WithHttpClient(httpClient),
+		githubfs.WithRepo("schmidtw", "githubfs"),
+	)
+
+	err := fs.WalkDir(gfs, "schmidtw/githubfs/git/main/.reuse",
+		func(path string, d fs.DirEntry, err error) error {
+			fmt.Printf("%s\n", path)
+			if err != nil || d.IsDir() {
+				return err
+			}
+
+			return nil
+		})
+	if err != nil {
+		panic(err)
+	}
+}
+```
+
+## Limitations
+
+- Symlinks are only supported for files fetched for small repos (where the fetch
+  occurs via a tarball).
+- Packages are not supported by the graphql API, so they aren't supported here.
+- Gists are not supported presently.