Added docs on running the linter

tools/readme_linter/README.md

@@ -0,0 +1,22 @@
+# README.md linter
+
+Run readme_linter with the filenames of the readme files you want to lint. For
+example:
+
+```shell
+~/go/src/github.com/influxdata/telegraf$ tools/readme_linter/readme_linter plugins/inputs/file/README.md
+```
+
+You can lint multiple filenames at once. This works well with shell globs.
+
+To lint all the plugin readmes:
+
+```shell
+~/go/src/github.com/influxdata/telegraf$ tools/readme_linter/readme_linter plugins/*/*/README.md
+```
+
+To lint readmes for inputs starting a-d:
+
+```shell
+~/go/src/github.com/influxdata/telegraf$ tools/readme_linter/readme_linter plugins/inputs/[a-d]*/README.md
+```