add protobuf to readme

README.md

@@ -6,12 +6,16 @@ This is a CATS RX-only I-Gate which can use a cheap SDR receiver to decode CATS
 
 ### Building
 
-To build the software, you will need to install [Rustup](https://rustup.rs/). You'll also need git. After these are installed, restart your terminal, or open a new one. Then run these commands:
+To build the software, you will need to install [Rustup](https://rustup.rs/). You'll also need to install some dependencies:
 
 ```bash
-sudo apt install rtl-sdr
+sudo apt install rtl-sdr git protobuf-compiler
 cargo install cargo-deb
+```
 
+After these are installed, restart your terminal, or open a new one. Then run these commands:
+
+```bash
 git clone https://gitlab.scd31.com/cats/sdr-igate
 cd sdr-igate
 git pull