docs: use mermaidjs for visual graphs

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Ib7ae49f209214fc428f6e9bfc5c7d9176a6a6964

README.md

@@ -81,8 +81,10 @@ Pre-built binaries are not yet available.
 For static sites served by Nginx, the proper setup is to place Eris in front of
 Nginx. Here is a graph of how it's meant to be configured:
 
-```
-Internet → [Eris (port 80)] → [Nginx (local port)]
+```mermaid
+graph LR
+    A[Internet] --> B[Eris (port 80)]
+    B --> C[Nginx (local port)]
 ```
 
 You will want to configure Eris to listen on port 80 (or 443 for SSL) and
@@ -132,8 +134,11 @@ eris --listen-addr 0.0.0.0:443 --backend-addr 127.0.0.1:8080 --ssl-cert /path/to
 
 ### Option 2: Use a separate SSL terminator
 
-```
-Internet → [SSL Terminator (port 443)] → [Eris (local port)] → [Nginx (local port)]
+```mermaid
+graph LR
+    A[Internet] --> B[SSL Terminator (port 443)]
+    B --> C[Eris (local port)]
+    C --> D[Nginx (local port)]
 ```
 
 You can use Nginx, HAProxy, or Caddy as the SSL terminator, forwarding decrypted