cln-tracer: readme usage clarifications

contrib/cln-tracer/README.md

@@ -6,12 +6,23 @@ This directory contains the following utilities:
 
  - `cln_tracer/trace.py` instruments and exports traces from a single binary.
 
+## Prerequisites
+
+`trace.py` sends traces to [zipkin](https://zipkin.io/), so zipkin needs to be
+installed.
+
 ## Installation
 
 Since the `bcc` library depends heavily on its binary extension
 matching the version of the kernel `systemtap-sdt-dev` version, it is
-strongly suggested to install the `libpbfcc` dependency via your
+strongly suggested to install the `libbpfcc` dependency via your
 package manager and _not_ use a virtualenv to run these tracers.
 
 The tracers also require kernel access, and will most likely have to
 be run by `root`
+
+## Usage
+To use with a default zipkin installation:
+```bash
+sudo python3 ./cln_tracer/trace.py http://127.0.0.1:9411/api/v2/spans /path/to/lightningd`
+```