Exclude *.txt files from the repository kotlin-hands-on#4

Author: hsz

.gitignore

@@ -1,3 +1,4 @@
 .gradle
 .idea
 build
+src/**/*.txt

README.md

@@ -51,6 +51,8 @@ After you create a new project based on the current template repository using th
     └── Utils.kt            A set of utility methods shared across your days
 ```
 
+> Note: All task input files are excluded from the repository with `.gitignore` – we should not post them publicly, as Eric Wastl asks for: [Tweet](https://twitter.com/ericwastl/status/1465805354214830081).
+
 When the first puzzle appears, go to the `Day01.kt` and for each `part1` and `part2` functions, provide an algorithm implementation using the `input` data loaded from the `src/Day01.txt` file.
 This input data is common for both parts, and you can find it on the bottom of each day on the [Advent of Code][aoc] page.