docs: add json, ndjson, checkstyle to "Available Formatters" (#1144)

README.md

@@ -94,6 +94,9 @@ Here's how `revive` is different from `golint`:
     - [Default](#default)
     - [Plain](#plain)
     - [Unix](#unix)
+    - [JSON](#json)
+    - [NDJSON](#ndjson)
+    - [Checkstyle](#checkstyle)
     - [SARIF](#sarif)
   - [Extensibility](#extensibility)
     - [Writing a Custom Rule](#writing-a-custom-rule)
@@ -597,9 +600,21 @@ The unix formatter produces the same output as the default formatter but surroun
 
 ![Unix formatter](/assets/formatter-unix.png)
 
+### JSON
+
+The `json` formatter produces output in JSON format.
+
+### NDJSON
+
+The `ndjson` formatter produces output in [`Newline Delimited JSON`](https://github.com/ndjson/ndjson-spec) format.
+
+### Checkstyle
+
+The `checkstyle` formatter produces output in a [Checkstyle-like](https://checkstyle.sourceforge.io/) format.
+
 ### SARIF
 
-The `sarif`  formatter produces outputs in SARIF, for _Static Analysis Results Interchange Format_, a standard JSON-based format for the output of static analysis tools defined and promoted by [OASIS](https://www.oasis-open.org/).
+The `sarif`  formatter produces output in SARIF, for _Static Analysis Results Interchange Format_, a standard JSON-based format for the output of static analysis tools defined and promoted by [OASIS](https://www.oasis-open.org/).
 
 Current supported version of the standard is [SARIF-v2.1.0](https://docs.oasis-open.org/sarif/sarif/v2.1.0/csprd01/sarif-v2.1.0-csprd01.html
 ).

config/config.go

@@ -101,16 +101,18 @@ var allRules = append([]lint.Rule{
 	&rule.RedundantBuildTagRule{},
 }, defaultRules...)
 
+// allFormatters is a list of all available formatters to output the linting results.
+// Keep the list sorted and in sync with available formatters in README.md.
 var allFormatters = []lint.Formatter{
-	&formatter.Stylish{},
+	&formatter.Checkstyle{},
+	&formatter.Default{},
 	&formatter.Friendly{},
 	&formatter.JSON{},
 	&formatter.NDJSON{},
-	&formatter.Default{},
-	&formatter.Unix{},
-	&formatter.Checkstyle{},
 	&formatter.Plain{},
 	&formatter.Sarif{},
+	&formatter.Stylish{},
+	&formatter.Unix{},
 }
 
 func getFormatters() map[string]lint.Formatter {