Added a README with useful infos.

README.md

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+# ESPleaf
+
+## Layout description
+
+Layout is defined in `LAYOUT` in `config.h`.
+
+LEDs within a node are supposed to be installed counter-clockwise. The edge where the cables enter the node is node 0. To its right (counter-clockwise, remember) is corner 0. Then edge 1, corner 1, edge 2, corner 2 before coming back to edge 0.
+
+Thereby, the next panel can either be installed along edge 1 or edge 2. (But the cable has to go corner 0, corner 1, corner 2 first.)
+
+First panel is ignored in `LAYOUT`. First entry in `LAYOUT` is the edge through which the cable leaves Node 0 to Node 1 - which can be either Edge 1 or Edge 2.
+
+On the next panel, the edge the cable is coming through is called Edge 0 again. And so on.
+
+So, `LAYOUT` countains a list of edges the cable takes to leave to the next node.
+
+## Commands
+
+Command can be sent via MQTT to `MQTT_TOPIC_COMMANDS`. Syntax is `key=value` or `key=value&key2=value2...`.
+
+Valid keys are:
+* `mode` sets a new mode. Valid modes are:
+  * `corners`
+  * `nodes`
+  * `first_corner`
+  * `first_node`
+  * `flash`
+  * `static`
+  * `off`
+* `brightness` sets the overall brightness of the lamp. Values are from 0 to 255 inclusive.
+* `duration` if sets, `mode` and `brightness` are set for this amount of seconds only.
+* `color` sets the color for `static` and `flash` modes. A predefined color name is expected.
+* `speedup` sets a speedup for faster animations. Default value 1, possible values are 1 to 255. 0 will lead to an exception.
+
+## Startup sequence
+
+During startup:
+* 1 green corner: FastLED is initialized. Layout is now being analyzed.
+* 2 green corners: Layout is done. WiFi is being connected.
+* 3 green corners: WiFi connection established. Connecting to MQTT server.
+* Everything green (quarter of a second): Initialization done.