add workdirbykey to readme

README.md

@@ -84,6 +84,7 @@ sudo ./out/sshpiperd --log-level=trace ./out/simplemath -- ./out/fixed --target
 Plugin list
 
  * [workingdir](plugin/workingdir/) 🔀: `/home`-like directory to managed upstreams routing by sshpiped.
+ * [workingdirbykey](plugin/workingdirbykey/) 🔀: same as `workingdir` but uses public key to route.
  * [azdevicecode](plugin/azdevicecode/) 🔒: ask user to enter [azure device code](https://docs.microsoft.com/en-us/azure/active-directory/develop/v2-oauth2-device-code) before login
  * [fixed](plugin/fixed/) 🔀: fixed targetting the dummy sshd server
  * [simplemath](plugin/simplemath/) 🔒: ask for very simple math question before login, demo purpose

plugin/workingdirbykey/README.md

@@ -0,0 +1,21 @@
+# Publickey based Working Directory plugin for sshpiperd
+
+This plugin is smilar to the [workingdir](../workingdir/) plugin, but it uses public key to route.
+
+workingdir tree
+
+```
+├── git
+│   ├── bitbucket
+│   │   └── sshpiper_upstream
+│   ├── github
+│   │   ├── authorized_keys
+│   │   ├── id_rsa
+│   │   └── sshpiper_upstream
+│   └── gitlab
+│       └── sshpiper_upstream
+├── linode....
+```
+
+The plugin will search across all sub directories of the `username` directory to see if the `downstream` key is in `authorized_keys` file.
+The first matched sub directory will be used to route to the upstream.