Update end-user README

Author: hsz

.github/template-cleanup/README.md

@@ -1,8 +1,27 @@
+![Tests](https://github.com/%REPOSITORY%/workflows/Tests/badge.svg)
+
 # %NAME%
 
-![Tests](https://github.com/%REPOSITORY%/workflows/Tests/badge.svg)
+Welcome to the Advent of Code[^aoc] Kotlin project created by [%NAME%][github] using the [Advent of Code Kotlin Template][template] delivered by JetBrains.
+
+In this repository, %NAME% is about to provide solutions for the puzzles using [Kotlin][kotlin] language.
+
+If you stuck with Kotlin-specific questions or anything related to this template, check out the following resources:
+
+- [Kotlin docs][docs]
+- [Kotlin Slack][slack]
+- Template [issue tracker][issues]
+
 
----
-Repository based on the [Advent of Code Kotlin Template][template].
+[^aoc]:
+    [Advent of Code][aoc] – an annual event in December since 2015.
+    Every year since then, with the first day of December, a programming puzzles contest is published every day for twenty-four days.
+    A set of Christmas-oriented challenges provide any input you have to use to answer using the language of your choice.
 
+[aoc]: https://adventofcode.com
+[docs]: https://kotlinlang.org/docs/home.html
+[github]: https://github.com/%NAME%
+[issues]: https://github.com/kotlin-hands-on/advent-of-code-kotlin-template/issues
+[kotlin]: https://kotlinlang.org
+[slack]: https://surveys.jetbrains.com/s3/kotlin-slack-sign-up
 [template]: https://github.com/hsz/advent-of-code-kotlin-template