tomll: port to v2 (#727)

Fixes #721

README.md

@@ -209,7 +209,7 @@ In case of trouble: [Go Modules FAQ][mod-faq].
 
 ## Tools
 
-Go-toml provides two handy command line tools:
+Go-toml provides three handy command line tools:
 
  * `tomljson`: Reads a TOML file and outputs its JSON representation.
 
@@ -225,6 +225,13 @@ Go-toml provides two handy command line tools:
     $ jsontoml --help
     ```
 
+ * `tomll`: Lints and reformats a TOML file.
+
+    ```
+    $ go install github.com/pelletier/go-toml/v2/cmd/tomll@latest
+    $ tomll --help
+    ```
+
 ## Migrating from v1
 
 This section describes the differences between v1 and v2, with some pointers on