[#453] Document how to make cross-compilation work with buildroot

[jerry-xie-000]

Notes for Reviewer

Refer to: #453.

Write the steps how to make cross-compilation work with buildroot.

Pre-Review Checklist for the PR Author

1. Add sensible notes for the reviewer
2. PR title is short, expressive and meaningful
3. Relevant issues are linked in the References section
4. Every source code file has a copyright header with SPDX-License-Identifier: Apache-2.0 OR MIT
5. Branch follows the naming format (iox2-123-introduce-posix-ipc-example)
6. Commits messages are according to this guideline
   • Commit messages have the issue ID ([#123] Add posix ipc example)
   • Commit author matches Eclipse Contributor Agreement (and ECA is signed)
7. Tests follow the best practice for testing
8. Changelog updated in the unreleased section including API breaking changes
9. Assign PR to reviewer
10. All checks have passed (except task-list-completed)

Checklist for the PR Reviewer

• Commits are properly organized and messages are according to the guideline
• Unit tests have been written for new behavior
• Public API is documented
• PR title describes the changes

Post-review Checklist for the PR Author

1. All open points are addressed and tracked via issues

References

Closes #453

[orecham]

Just a couple of nitpicks. You will also need to register an eclipse account and sign the ECA agreement since we are an eclipse project.

Markdown linting might also bite you, but you can run this script to help: ./internal/scripts/check_markdown_linting.sh --fix

Could you also please fill out the PR template and ensure the open items are addressed, e.g. the commit needs to be prefixed with the issue number for traceability: [#453] Document how to make cross-compilation work with buildroot

[orecham]

Suggested change

	8. cd iceoryx2
	8. Change to the iceoryx2 directory
	```console
	cd iceoryx2
	```
	9 ...

Could you put these instructions in code blocks to make it easier to copy the steps.

[orecham]

Suggested change

	Finally, you can get the arm64 libs, include files in _OUTPUT folder.
	Finally, you can get the arm64 libs, include files in the `_OUTPUT` folder.

[orecham]

Suggested change

	2. install the `rust` tool: `curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh`
	2. install the `rust` toolchain: `curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh`