Update README with available blocks

Author: milanofthe

README.md

@@ -21,9 +21,14 @@
 
 PathSim-RF extends the [PathSim](https://github.com/pathsim/pathsim) simulation framework with blocks for RF and microwave engineering. All blocks follow the standard PathSim block interface and can be connected into simulation diagrams.
 
-## Features
-
-*Coming soon.*
+## Blocks
+
+| Block | Description | Key Parameters |
+|-------|-------------|----------------|
+| `RFNetwork` | N-port network from S-parameter data (Touchstone) via vector fitting | `ntwk`, `auto_fit` |
+| `TransmissionLine` | Lossy delay-based transmission line (scattering domain) | `length`, `er`, `attenuation`, `Z0` |
+| `RFAmplifier` | Amplifier with optional IP3 nonlinearity | `gain` [dB], `IIP3` [dBm], `P1dB` [dBm], `Z0` |
+| `RFMixer` | Ideal frequency converter (time-domain multiplication) | `conversion_gain` [dB], `Z0` |
 
 ## Install