docs: add example

README.md

@@ -1,2 +1,24 @@
 # fast-log
-High-performance logger with lock-free ring buffer
+High-performance logger with lock-free ring buffer, use this library when you want to log in the hotpath and performance is critical.
+
+## Example
+Submitting a log to either stdout or a file is very simple, you just give a closure which evaluates to a string. This is extremely fast, usually less than 100 nanos. A simple example:
+
+```rust
+let o = LoggerFileOptions {
+    path: "log.txt",
+    append_mode: false, // should the logger just append to what's already there or overwrite?
+};
+
+// The size is bounded, issuing a new log when the ringbuffer is full will block.
+let logger = Logger::new(1024 * 8, Some(o));
+
+// Log to stdout
+logger.log(|| format!("To stdout: {}", 42));
+
+// Log to the file, format_log! will prepend the file and LOC location to the log.
+logger.log_f(|| format_log!("To log.txt {}", 5)); // path/to/file:LINE: To log.txt 5
+
+// Blocks until all logs are handled.
+logger.shutdown();
+```