structure gardening tool

tools/gardening/README.md

 # Gardening Tools
 
 This directory is created for gathering all tools doing gardening in one place.
 Every tools or script, big or small should go here, and over time, hopefully
 we will have useful collection of tools that support every part of the 
 gardening work.
 
 The current tools are:
 
 #### compare_failures ####
 Compares the test log of a build step with previous builds. Use this to detect 
 flakiness of failures, especially timeouts.
 
 Usage:
 
-    dart compare_failures.dart <stdio-url>
-    
+```console
+dart bin/compare_failures.dart <stdio-url>
+```
+
 where `<stdio-url>` is a url for a test log (".../logs/stdio") from the 
 buildbot. 
 
 #### status_summary ####
 Collects the configurations for all status files in the 'tests' folder that
 mention one of the test names given as argument.
 
 Usage:
 
-    dart status_summary.dart <test-name1> [<test-name2> ...]
-    
+```console
+dart bin/status_summary.dart <test-name1> [<test-name2> ...]
+```
+
 where `<test-nameX>` are test names like `language/arithmetic_test`.
 
 #### current_summary ####
 Collects the test results for all build bots in [buildGroups] for tests
 that mention one of the test names given as argument.
 
 Usage:
 
-    dart current_summary.dart <test-name1> [<test-name2> ...]
-    
+```console
+dart bin/current_summary.dart <test-name1> [<test-name2> ...]
+```
+
 where `<test-nameX>` are test names like `language/arithmetic_test`.
 
 The results are currently pulled from the second to last build since the
 last build might not have completed yet.