Mention locales in DateTime concept

This updates the date time concept to mention different Locales can be
used with the DateTimeFormatter. Locales is needed to solve the
corresponding Booking for Beauty exercise, so it would be helpful for
students to be aware of this.

Resolves #3088

Author: kahgoh

concepts/datetime/.meta/config.json

@@ -1,5 +1,9 @@
 {
   "blurb": "There are several classes in Java to work with dates and time.",
-  "authors": ["sanderploegsma"],
-  "contributors": []
+  "authors": [
+    "sanderploegsma"
+  ],
+  "contributors": [
+    "kahgoh"
+  ]
 }

concepts/datetime/about.md

@@ -118,7 +118,18 @@ printer.format(date);
 // => "December 3, 2007"
 ```
 
+A [locale][locale] can also be specified when creating the custom format to format and parse for different regions:
+
+```java
+DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.FRENCH).format(date);
+// => décembre 3, 2007
+
+DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.of("pt")).format(date);
+// => dezembro 3, 2007
+```
+
 [iso-8601]: https://en.wikipedia.org/wiki/ISO_8601
 [localdate-docs]: https://docs.oracle.com/javase/8/docs/api/java/time/LocalDate.html
 [localdatetime-docs]: https://docs.oracle.com/javase/8/docs/api/java/time/LocalDateTime.html
+[locale]: https://docs.oracle.com/javase/8/docs/api/java/util/Locale.html
 [datetimeformatter-docs]: https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html

concepts/datetime/introduction.md

@@ -86,4 +86,14 @@ printer.format(date);
 // => "December 3, 2007"
 ```
 
+A locale can also be specified when creating the custom format to format and parse for different regions:
+
+```java
+DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.FRENCH).format(date);
+// => décembre 3, 2007
+
+DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.of("pt")).format(date);
+// => dezembro 3, 2007
+```
+
 [iso-8601]: https://en.wikipedia.org/wiki/ISO_8601

exercises/concept/booking-up-for-beauty/.docs/introduction.md

@@ -88,4 +88,14 @@ printer.format(date);
 // => "December 3, 2007"
 ```
 
+A locale can also be specified when creating the custom format to format and parse for different regions:
+
+```java
+DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.FRENCH).format(date);
+// => décembre 3, 2007
+
+DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.of("pt")).format(date);
+// => dezembro 3, 2007
+```
+
 [iso-8601]: https://en.wikipedia.org/wiki/ISO_8601