docs: extend prettier config docs

Author: simschla

README.md

@@ -134,7 +134,7 @@ Runs spotless
 Available formatting steps:
   license-header      Runs license header
   google-java-format  Runs google java format
-  prettier            Runs prettier
+  prettier            Runs prettier, the opinionated code formatter.
 ```
 
 <!---freshmark /usage_main -->
@@ -284,23 +284,27 @@ Usage: spotless prettier [-hV] [-C=<cacheDir>] [-n=<explicitNpmExecutable>]
                          [-N=<explicitNodeExecutable>]
                          [-P=<prettierConfigPath>] [-R=<explicitNpmrcFile>]
                          [-A=<additionalNpmrcLocations>]...
-                         [-c=<String=String>]... [-D=<String=String>]...
-Runs prettier
+                         [-c='OPTION=VALUE']... [-D='PACKAGE=VERSION']...
+Runs prettier, the opinionated code formatter.
   -A, --additional-npmrc-location=<additionalNpmrcLocations>
                   Additional locations to search for .npmrc files.
-  -c, --prettier-config-option=<String=String>
-                  The Prettier configuration options.
+  -c, --prettier-config-option='OPTION=VALUE'
+                  A prettier configuration options.
+                    The format is 'OPTION=VALUE'.
+                    example: 'printWidth=80'
   -C, --cache-dir=<cacheDir>
-                  The directory to use for caching Prettier.
-  -D, --dev-dependency=<String=String>
-                  The devDependencies to use for Prettier.
+                  The directory to use for caching prettier.
+  -D, --dev-dependency='PACKAGE=VERSION'
+                  An entry to add to the package.json for running prettier.
+                    The format is 'PACKAGE=VERSION'.
+                    example: 'prettier=2.8.7'
   -h, --help      Show this help message and exit.
   -n, --npm-exec=<explicitNpmExecutable>
                   The explicit path to the npm executable.
   -N, --node-exec=<explicitNodeExecutable>
                   The explicit path to the node executable.
   -P, --prettier-config-path=<prettierConfigPath>
-                  The path to the Prettier configuration file.
+                  The path to the prettier configuration file.
   -R, --npmrc-file=<explicitNpmrcFile>
                   The explicit path to the .npmrc file.
   -V, --version   Print version information and exit.

app/src/main/java/com/diffplug/spotless/cli/steps/Prettier.java

@@ -37,19 +37,22 @@
 import static com.diffplug.spotless.cli.core.FilePathUtil.asFile;
 import static com.diffplug.spotless.cli.core.FilePathUtil.asFiles;
 import static com.diffplug.spotless.cli.core.FilePathUtil.assertDirectoryExists;
+import static com.diffplug.spotless.cli.help.OptionConstants.NEW_LINE;
 import static com.diffplug.spotless.cli.steps.OptionDefaultUse.use;
 
-@CommandLine.Command(name = "prettier", description = "Runs prettier")
+@CommandLine.Command(name = "prettier", description = "Runs prettier, the opinionated code formatter.")
 public class Prettier extends SpotlessFormatterStep {
 
     @CommandLine.Option(
             names = {"--dev-dependency", "-D"},
-            description = "The devDependencies to use for Prettier.")
+            description = "An entry to add to the package.json for running prettier." + NEW_LINE
+                    + "The format is @|YELLOW 'PACKAGE=VERSION'|@." + NEW_LINE + "example: 'prettier=2.8.7'",
+            paramLabel = "'PACKAGE=VERSION'")
     Map<String, String> devDependencies;
 
     @CommandLine.Option(
             names = {"--cache-dir", "-C"},
-            description = "The directory to use for caching Prettier.")
+            description = "The directory to use for caching prettier.")
     Path cacheDir;
 
     @CommandLine.Option(
@@ -74,12 +77,14 @@ public class Prettier extends SpotlessFormatterStep {
 
     @CommandLine.Option(
             names = {"--prettier-config-path", "-P"},
-            description = "The path to the Prettier configuration file.")
+            description = "The path to the prettier configuration file.")
     Path prettierConfigPath;
 
     @CommandLine.Option(
             names = {"--prettier-config-option", "-c"},
-            description = "The Prettier configuration options.")
+            description = "A prettier configuration options." + NEW_LINE + "The format is @|YELLOW 'OPTION=VALUE'|@."
+                    + NEW_LINE + "example: 'printWidth=80'",
+            paramLabel = "'OPTION=VALUE'")
     Map<String, String> prettierConfigOptions;
 
     @NotNull @Override