feat(count-files): add subject, test and solution for the exercise count-files

sh/tests/count-files_test.sh

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+#!/usr/bin/env bash
+
+# Unofficial Bash Strict Mode
+set -euo pipefail
+IFS='
+'
+
+script_dirS=$(cd -P "$(dirname "$BASH_SOURCE")" &>/dev/null && pwd)
+
+challenge() {
+    submitted=$(cd "$1" && bash "$script_dirS"/student/count-files.sh)
+    expected=$(cd "$1" && bash "$script_dirS"/solutions/count-files.sh)
+
+    diff <(echo "$submitted") <(echo "$expected")
+}
+
+challenge cl-camp5/folder1
+challenge cl-camp5/folder2

sh/tests/solutions/count-files.sh

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+#!/usr/bin/env bash
+
+find . -type d,f | wc -l

subjects/count-files/README.md

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+## Count files
+
+### Instructions
+
+Create a file `count-files.sh`, which will print the number **(and only the number)** of regular files and folders contained in the current directory and its sub-folders (the current directory must be included in the count):
+
+### Usage
+
+```console
+$ ./count-files.sh | cat -e
+12$
+$
+```
+
+**Tips:**
+
+Here are some Commands that can help you:
+
+- `find`. Find files or directories under the given directory tree, recursively. [For more information](https://manned.org/find).
+- `wc`. Count lines, words, and bytes. [For more information](https://www.gnu.org/software/coreutils/wc).
+
+Use the man to get more info on the commands `find` and `wc`.