initial Docker readme

docker/README.md

@@ -0,0 +1,42 @@
+# Building
+
+docker build --pull --rm -t postfixadmin-image .
+
+# Running
+
+## No config.local.php / no existing setup
+
+If you do not have a config.local.php, then we fall back to look for environment variables to generate one.
+
+POSTFIXADMIN\_DB\_TYPE can be one of :
+
+ * mysqli
+ * pgsql
+ * sqlite
+
+
+```bash
+docker run -e POSTFIXADMIN_DB_TYPE=mysqli \
+           -e POSTFIXADMIN_DB_HOST=whatever \
+           -e POSTFIXADMIN_DB_USER=user \
+           -e POSTFIXADMIN_DB_PASSWORD=topsecret \
+           -e POSTFIXADMIN_DB_NAME=postfixadmin \
+           --name postfixadmin \
+           -p 8080:80 \
+        postfixadmin-image
+```
+
+Note: An sqlite database is used as a fallback if you do not have a config.local.php and do not specify the above variables.
+
+
+
+## Existing config.local.php 
+
+```bash
+docker run --name postfixadmin -p 8080:80 postfixadmin-image
+```
+
+## Linking to a MySQL or PostgreSQL container
+
+If you link the container to a MySQL or PostgreSQL container, then we attempt to generate a valid config.local.php from it. 
+