docs: add a section about pino-logfmt (#1941)

docs/transports.md

@@ -423,6 +423,7 @@ PRs to this document are welcome for any new transports!
 + [pino-opentelemetry-transport](#pino-opentelemetry-transport)
 + [@axiomhq/pino](#@axiomhq/pino)
 + [pino-discord-webhook](#pino-discord-webhook)
++ [pino-logfmt](#pino-logfmt)
 
 ### Legacy
 
@@ -1047,6 +1048,21 @@ const logger = pino({
 })
 ```
 
+<a id="pino-logfmt"></a>
+### pino-logfmt
+
+[pino-logfmt](https://github.com/botflux/pino-logfmt) is a Pino v7+ transport that formats logs into [logfmt](https://brandur.org/logfmt). This transport can output the formatted logs to stdout or file.
+
+```js
+import pino from 'pino'
+
+const logger = pino({
+  transport: {
+    target: 'pino-logfmt'
+  }
+})
+```
+
 <a id="communication-between-pino-and-transport"></a>
 ## Communication between Pino and Transports
 Here we discuss some technical details of how Pino communicates with its [worker threads](https://nodejs.org/api/worker_threads.html).