Add README with building instructions

tracetools/README.md

@@ -0,0 +1,26 @@
+# tracetools
+
+## Building
+
+If tracing is not enabled when building, or if LTTng is not found, then this package will not do anything.
+
+To enable tracing:
+
+1. Install [LTTng](https://lttng.org/docs/v2.10/#doc-ubuntu):
+    ```
+    $ sudo apt-get install lttng-tools lttng-modules-dkms liblttng-ust-dev
+    ```
+2. Build with the `WITH_LTTNG` flag:
+    ```
+    $ colcon build --cmake-args " -DWITH_LTTNG=ON"
+    ```
+3. Check if tracing is enabled (after sourcing):
+    ```
+    $ ros2 run tracetools tracetools_status
+    ```
+
+## Tracing
+
+By default, the steps above will not lead to trace data being generated, and thus they will have no impact on execution.
+
+LTTng has to be enabled: TODO mention scripts