Installation updated

README.md

@@ -11,11 +11,14 @@ APRS (text msg + geo-coordinates + meta-data) -> AX.25 -> PCM -> PWM -> Band-Pas
 
 Both a static library `libaprs_pico.a` and an example application will be generated by the build.
 
+![AFSK scope screenshot](https://github.com/eleccoder/raspi-pico-aprs-tnc/blob/main/doc/img/afsk_scope.png "Scope screenshot of an AFSK output signal")
+
 ## Preliminaries
 
 Your host platform is assumed to be LINUX.
-If you have already installed the Pico-SDK, set the `PICO_SDK_PATH` environment variable accordingly to avoid installing the SDK twice.
 
+1. Install the Pico-SDK following the instructions given in the [Raspberry Pi 'Getting Started' Guide](https://datasheets.raspberrypi.org/pico/getting-started-with-pico.pdf) (pdf)
+1. Set the `PICO_SDK_PATH` environment variable to point to your Pico-SDK installation directory
 
 ## Hardware
 
@@ -23,7 +26,6 @@ We just need a simple band-pass filter to extract the AFSK-signal from the PWM s
 
 ![band-pass filter](https://github.com/eleccoder/raspi-pico-aprs-tnc/blob/main/doc/schematic/band_pass_filter.png)
 
-
 ## Build the library and the example application
 
 ```
@@ -43,9 +45,6 @@ cd build
 
 The GPIO-pin 'GP0' is the line-out for the analog AFSK-signal. You can observe it by using a scope, listen to it by using an audio amp, or connect it to any RF transceiver to send it on the air (ham radio license required).
 
-![AFSK scope screenshot](https://github.com/eleccoder/raspi-pico-aprs-tnc/blob/main/doc/img/afsk_scope.png "Scope screenshot of an AFSK output signal")
-
-
 ## TODO (Aug 2021)
 
 - [x] Thorough evaluation, in general
@@ -53,7 +52,6 @@ The GPIO-pin 'GP0' is the line-out for the analog AFSK-signal. You can observe i
 - [x] Show how to connect to a Baofeng HT
 - [x] PTT control for RF tranceivers
 
-
 ## Acknowledgements
 
 - For APRS => AX.25 conversion I'm using a [modified version](https://github.com/eleccoder/ax25-aprs-lib) of [fsphil's ax25beacon](https://github.com/fsphil/ax25beacon)