update readme to markdown file

readme.md

@@ -1,17 +1,15 @@
-sus
-===
+# sus
 
 simple URL shortener
 
 
-usage
------
+## usage
 
-creating a new shortlink at https://pls.cx/shortlink
+- creating a new shortlink at https://pls.cx/shortlink
 
 	susmng [-s pls.cx] create -l shortlink -v https://example.com
 
-deleting the shortlink https://pls.cx/shortlink
+- deleting the shortlink https://pls.cx/shortlink
 
 	susmng [-s pls.cx] delete -l shortlink -v confirm
 
@@ -19,10 +17,9 @@ susmng will assume the first server in the 'secrets' section if the -s flag is
 not provided.
 
 
-installation
-------------
+## installation
 
-running the server
+### running the server
 
 1. generate the secret used to create and delete shortlinks
 
@@ -32,7 +29,12 @@ running the server
 
 	docker-compose up -d --build
 
-setting up susmng
+#### server environment variables
+
+- `SECRET` - the secret used for signature verification
+- `LISTEN_ADDRESS` - the address the server is listening on (default is `0.0.0.0:80`)
+
+### setting up susmng
 
 1. install susmng