Evaluate remaining red/green time for upcoming intersection

Readme.md

@@ -2,6 +2,29 @@
 
 Displays different C-ITS receive-only use cases for cheap.
 
+## Hardware Requirements
+The code is currently tailored to:
+- Seeed XIAO ESP32-C5 (8MB PSRAM)
+- Seeed XIAO L67K (connected on GPIO12 (RX), GPIO11 (TX), GPIO1 (wakeup) and GPIO25 (reset))  
+TODO: only enable in `spat` feature?
+- TODO: display (when using `spat` feature)
+
+## Features
+
+### SPAT
+Takes the current position and heading from the GNSS receiver and displays the signal phases of the upcoming intersection.
+The upcoming intersection is selected when the own position is "inside" some ingress approach of the intersection.
+The display will show the current phase and remaining time for all signal groups of the bike-able lanes in the approach.
+
+### DENM
+TODO: Not implemented yet!
+
+Shall "publish" the most relevant information of a DENMs via BLE
+
+### CAM
+Just prints a line for each received CAM.
+
+
 ## Usage
 
 ### Toolchain Installation
@@ -24,10 +47,23 @@ rustup component add --toolchain nightly rustfmt
 ```
 
 ### Build and Flash
+In default configuration only signal phases (SPAT) data is displayed for the upcoming intersection.
+Additional features are available though feature flags:
+
+- `esp`: Run on ESP (required as feature flag to enable unit tests on host)
+- `std`: Run on system with `std` library
+- `spat`: Enable signal phase (and intersection map) data  
+- `denm`: Enable DENMs
+- `cam`: Enable CAMs
+
 Connect your ESP32-C5 and run:
 
 ```
+# default configuration
 cargo run --release
+
+# for e.g. also enable DENM feature
+cargo run --release -F denm
 ```
 
 ### Run Unit Tests on Host