feat(file-struct): add subject, test and solution for new a exercise

sh/tests/file-struct_test.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+# Unofficial Bash Strict Mode
+set -euo pipefail
+IFS='
+'
+
+print_content() {
+    mkdir -p uncompressed
+    tar -xpf done.tar -C uncompressed
+    tree uncompressed
+}
+
+submitted=$(cd student/struct && print_content)
+expected=$(cd solutions/struct && print_content)
+diff <(echo "$submitted") <(echo "$expected")

subjects/file-struct/README.md

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+## File struct
+
+In order to create new directories or folders in Linux or Unix-like operating systems you need to use the `mkdir` command. `mkdir` stands for “make directory.” you can use it like so:
+
+```console
+User-> mkdir my_folder
+User-> ls
+my_folder
+```
+
+### Instructions
+
+Create the files and directories so that when you use the command `tree` below, the output will look like this:
+
+```console
+User -> tree struct/
+struct/
+├── 0
+├── 1
+├── 2
+├── 3
+│   └── text.txt
+├── 4
+│   └── text2.txt
+├── 5
+├── 6
+├── 7
+├── 8
+├── 9
+└── A
+    └── text3.txt
+```
+
+Once it is done, use the command below to create the file `done.tar` to be submitted.
+
+```console
+User-> tar -cf done.tar *
+User-> ls
+0  1  2  3  4  5  6  7  8  9  A  done.tar
+```
+
+**Only `done.tar` should be submitted.**
+
+**Tips:**
+
+Use the command `man mkdir` to get more info.