diff --git a/doc/Overview.png b/doc/Overview.png
new file mode 100644
index 0000000..29c43d0
Binary files /dev/null and b/doc/Overview.png differ
diff --git a/doc/Overview.xml b/doc/Overview.xml
new file mode 100644
index 0000000..df1e056
--- /dev/null
+++ b/doc/Overview.xml
@@ -0,0 +1 @@
+<mxfile modified="2019-02-07T21:27:44.686Z" host="www.draw.io" agent="Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:65.0) Gecko/20100101 Firefox/65.0" etag="tnhgfPkYZ02dah6ygGXB" version="10.1.9" type="device"><diagram name="Page-1" id="5f0bae14-7c28-e335-631c-24af17079c00">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</diagram></mxfile>
\ No newline at end of file
diff --git a/doc/dev.md b/doc/dev.md
index 61dd3f1..83ba3c0 100644
--- a/doc/dev.md
+++ b/doc/dev.md
@@ -1,5 +1,4 @@
 
-```sql
-update blocks set mtime = 0 where pos = (select max(pos) from blocks);
-select max(mtime) from blocks;
-```
+# System overview
+
+<img src="./Overview.png">
\ No newline at end of file
diff --git a/readme.md b/readme.md
index 4b855c7..fce9796 100644
--- a/readme.md
+++ b/readme.md
@@ -10,6 +10,7 @@ Realtime mapserver for [Minetest](https://minetest.net)
 * [Parameters](doc/params.md)
 * [Configuration](doc/config.md)
 * [Contribution](doc/contrib.md)
+* [Development](doc/dev.md)
 
 # Features
 
@@ -27,6 +28,10 @@ Realtime mapserver for [Minetest](https://minetest.net)
 * Street names / Train stuff
 * City borders
 
+# Supported databases
+
+* Sqlite3 (for map and mapobjects)
+
 # Development state
 
 * Working basic features (map rendering)