README.md add trace crate si_trace_print

add to README a section about tracing crate `si_trace_print`

README.md

@@ -236,6 +236,11 @@ The problem here is that rust does not support 'non-inline modules in proc macro
 
 There is an [old implementation](https://github.com/gsingh93/trace/tree/4622ab5d5141d126dd02f66f89f20fd891e73a9d) of this crate which still uses the compiler plugin interface. Problem: The interal AST is quite unstable and the crates code would need to be adapted often to keep up.
 
+### si_trace_print
+
+[si_trace_print](https://crates.io/crates/si_trace_print) is "stack indented trace printing". It is rust library that requires macro statements to print messages. The messages are indented to stack depth and may be optionally preceded by the function name.
+
+The aim of `si_trace_print` is to be a simple "entry-level" tracing library to aid developers manually reviewing singular program runs.
 
 ### hawktracer-rust:
 [hawktracer-rust](https://www.hawktracer.org/) ([GitHub](https://github.com/AlexEne/rust_hawktracer)) provides rust-bindings for Amazons hawktracer. This requires annotating your code with tracepoints, but looks like a nice solution if that is what you want.
@@ -329,4 +334,4 @@ at your option.
 
 Unless you explicitly state otherwise, any contribution intentionally submitted
 for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
-dual licensed as above, without any additional terms or conditions.
+dual licensed as above, without any additional terms or conditions.