Add Hello nf-core training course

docs/hello_nf-core/00_orientation.md

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+# Orientation
+
+## GitHub Codespaces
+
+The GitHub Codespaces environment contains all the software, code and data necessary to work through this training course, so you don't need to install anything yourself.
+However, you do need a (free) GitHub account to log in, and you should take a few minutes to familiarize yourself with the interface.
+
+If you have not yet done so, please go through the [Environment Setup](../../envsetup/) mini-course before going any further.
+
+## Working directory
+
+Throughout this training course, we'll be working in the `hello-nf-core/` directory.
+
+Change directory now by running this command in the terminal:
+
+```bash
+cd hello-nf-core/
+```
+
+!!!tip
+
+    If for whatever reason you move out of this directory, you can always use the full path to return to it, assuming you're running this within the Github Codespaces training environment:
+
+    ```bash
+    cd /workspaces/training/hello-nf-core
+    ```
+
+Now let's have a look at the contents of this directory.
+
+## Materials provided
+
+You can explore the contents of this directory by using the file explorer on the left-hand side of the training workspace.
+Alternatively, you can use the `tree` command.
+
+Throughout the course, we use the output of `tree` to represent directory structure and contents in a readable form, sometimes with minor modifications for clarity.
+
+Here we generate a table of contents to the second level down:
+
+```bash
+tree . -L 2
+```
+
+If you run this inside `hello-nf-core`, you should see the following output:
+
+```console title="Directory contents"
+.
+├── ...
+├── solutions
+│   ├── 1-...
+└── ...
+
+X directories, Y files
+```
+
+**Here's a summary of what you should know to get started:**
+
+- [...]
+
+- **The `solutions` directory** contains the completed workflow scripts that result from each step of the course.
+  They are intended to be used as a reference to check your work and troubleshoot any issues.
+  The name and number in the filename correspond to the step of the relevant part of the course.
+  For example, [...]
+
+**Now, to begin the course, click on the arrow in the bottom right corner of this page.**