Add asciiflow diagram to the csi-proxy

borrowed from @ddebroy 's slack message, added some metadata.  Also added example files to look at to make it easier to grok the way its used by looking at SMB/Azure File implementations

Author: jayunit100

README.md

@@ -1,9 +1,39 @@
 # CSI Proxy
 
-CSI Proxy is a binary that exposes a set of gRPC APIs around storage operations
-over named pipes in Windows. A container, such as CSI node plugins, can mount
-the named pipes depending on operations it wants to exercise on the host and
-invoke the APIs.
+CSI Proxy (which might be more aptly named "csi-node-proxy") is a binary that exposes a set of gRPC APIs around local storage operations for nodes in Windows. A container, such as CSI node plugins, can mount the named pipes depending on operations it wants to exercise on the host and
+invoke the APIs.  This allows a storage plugin to run as if were a CSI plugin on linux which had the ability to do "priveleged" actions on the windows host OS.
+
+```
+                                              +------------------+
++---------------------------------------------|                  |
+|                 +----------+                |                  |
+|                 |csi node  |                |   CSI Node Plugin|
+|                 |driver    +---------------->                  |
+|                 |registrar |                |                  |
+| NodeStageVolume ----^------+                ----------+--------+
+| NodeUnstageVol      |                                 |  Disk APIs
+| NodePublishVol      |GetNodeInfo                      |  Volume APIs
+| NodeResizeVol       |NodeRegistrationStatus    /pipe  |  SMB APIs
+| NodeGetInfo         |                                 |  FileSystem/System APIs
+| NodeGetVolStats     | csi-plugin-reg.sock   +---------v---------+
+|                     |                       |                   |
+|                 + --+--------+              |    csi-proxy.exe  |
+|                 | kubelet.exe|              +-------------------+
+|                 |            |                      |
+|                 +---+--------++                     |
+|                     |                               |
+| csi.sock            |                               |
+|                     v                               v
+|                 +---+-------------------------------+------+
+|                 |                                          |
++---------------->|         Host Os (Windows)                |
+                  +------------------------------------------++
+```
+In the above diagram, there are 3 communication channels being utilized for CSI proxy:
+
+- `csi.sock` : This lives at /var/lib/kubelet/plugins/csi-plugin/csi.sock, and is used for the host OS to communicate with the CSI node plugin
+- `csi-plugin-reg.sock` : This lives here, /var/lib/kubelet/plugins_registry/csi-plugin-reg.sock, and is used for the kubelet itself to get metadata as needed from the csi plugin  
+- `/pipe` : /pipe/csi-proxy-api-group-v-... : This pipe lives at \pipe\csi-proxy-api-group-v-..., upon receipt of specific requests from the Node plugin, it carries out actions on the node plugins behalf.  Since it doesn't execute arbitrary commands on the host, its more secure then simply being a black-box proxy to run host commands.
 
 Each named pipe will support a specific version of an API (e.g. v1alpha1, v2beta1)
 that targets a specific area of storage (e.g. disk, volume, file, SMB, iSCSI).
@@ -143,11 +173,11 @@ You can reach the maintainers of this project at:
 
 ## Supported CSI Drivers
 
-- [SMB CSI Driver](https://github.com/kubernetes-csi/csi-driver-smb/tree/master/deploy/example/windows)
+- [SMB CSI Driver](https://github.com/kubernetes-csi/csi-driver-smb/tree/master/deploy/example/windows). To see specifically how this driver is invoked, you can look at https://github.com/kubernetes-csi/csi-driver-smb/blob/master/pkg/mounter/safe_mounter_windows.go.
 
 - [Azure Disk CSI Driver](https://github.com/kubernetes-sigs/azuredisk-csi-driver/tree/master/deploy/example/windows)
 
-- [Azure File CSI Driver](https://github.com/kubernetes-sigs/azurefile-csi-driver/tree/master/deploy/example/windows)
+- [Azure File CSI Driver](https://github.com/kubernetes-sigs/azurefile-csi-driver/tree/master/deploy/example/windows).  See https://github.com/kubernetes-sigs/azurefile-csi-driver/blob/master/pkg/mounter/safe_mounter_windows.go as an example of the invocation path
 
 - [Google Compute Engine Persistent Disk CSI Driver](https://github.com/kubernetes-sigs/gcp-compute-persistent-disk-csi-driver)