Add architecture diagram to deployment.md. (#296)

Also add a note that voting wallets should not be run on the
web server.

README.md

@@ -6,7 +6,7 @@
 
 ## Overview
 
-<img src="./docs/stakey.png" align="right" />
+<img src="./docs/img/stakey.png" align="right" />
 
 vspd is a from scratch implementation of a Voting Service Provider (VSP) for
 the Decred network.

docs/deployment.md

@@ -4,6 +4,10 @@ This guide is deliberately written at a high level and with minimal details
 because it is assumed that VSP operators will already have a level of
 familiarity with Decred software and a level of sysadmin experience.
 
+<p align="center">
+  <img src="./img/architecture.png">
+</p>
+
 ## Prerequisites
 
 ### Build from source
@@ -45,7 +49,7 @@ front-end server must be able to reach each instance of dcrwallet over RPC.
 
 The front-end server is where vspd will be running. A webserver (eg. nginx)
 should be configured with SSL and used to proxy requests from the internet to
-vspd.
+vspd. **Do not run a voting wallet on your webserver.**
 
 1. Start an instance of dcrd on this server with transaction index enabled
    (`--txindex`). dcrd is used for fishing ticket details out of the chain, for
@@ -59,9 +63,9 @@ vspd.
 1. A vspd database must be initialized before vpsd can be started. To do this,
    provide vspd with the xpub key it should use for collecting fees:
 
-  ```no-highlight
+    ```no-highlight
-  $ vspd --feexpub=tpubVppjaMjp8GEW...
+    $ vspd --feexpub=tpubVppjaMjp8GEW...
-  ```
+    ```
 
 1. Once the database is initialized, vspd can be started for normal operation by
    running it without the `--feexpub` flag.

docs/img/architecture-source.md

@@ -0,0 +1,38 @@
+Below is the source for architecture.png in mermaid.js syntax.
+
+Can be rendered with any mermaid.js deployment, for example <https://mermaid-js.github.io/mermaid-live-editor/>.
+
+```no-highlight
+%%{init:{
+    "theme": "neutral",
+    "themeVariables": {
+        "fontSize": "16px",
+        "clusterBkg": "#E9F8FE",
+        "clusterBorder": "#3D5873",
+        "mainBkg": "#2DD8A3",
+        "primaryColor": "#2970FF"
+    }
+}}%%
+
+graph LR
+
+subgraph Front-end Server
+    nginx(nginx) --> vspd(vspd)
+    vspd --> dcrd0(dcrd)
+end
+
+subgraph voting3 [Voting Server 3]
+    dcrwallet3(dcrwallet) --> dcrd3(dcrd)
+end
+
+subgraph voting2 [Voting Server 2]
+    dcrwallet2(dcrwallet) --> dcrd2(dcrd)
+end
+
+subgraph voting1 [Voting Server 1]
+    dcrwallet1(dcrwallet) --> dcrd1(dcrd)
+end
+
+vspd ----> dcrwallet1 & dcrwallet2 & dcrwallet3
+web(Internet<br />Traffic) ---> nginx
+```