docs(architectures): reword how to section

[mr-cal]

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• Have you successfully run make lint?
• Have you successfully run pytest tests/unit?

---

Use more accurate wording for building for a different architecture. Remove 'cross-compiling' because snapcraft doesn't automatically cross-compile.

From @cmatsuoka's suggestion in #4336 (comment)

[codecov-commenter]

Codecov Report

Merging #4362 (cf67177) into main (061b4f0) will decrease coverage by 5.67%.
Report is 86 commits behind head on main.
The diff coverage is 93.15%.

❗ Current head cf67177 differs from pull request most recent head 36beaf8. Consider uploading reports for the commit 36beaf8 to get more accurate results

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@@            Coverage Diff             @@
##             main    #4362      +/-   ##
==========================================
- Coverage   94.88%   89.22%   -5.67%     
==========================================
  Files         658      301     -357     
  Lines       55138    20688   -34450     
==========================================
- Hits        52319    18458   -33861     
+ Misses       2819     2230     -589     

Files Changed	Coverage Δ
snapcraft/elf/elf_utils.py	95.38% <ø> (ø)
snapcraft/legacy_cli.py	55.55% <ø> (+2.92%)	⬆️
snapcraft/projects.py	96.33% <ø> (ø)
snapcraft_legacy/__init__.py	90.90% <ø> (-0.40%)	⬇️
snapcraft_legacy/_store.py	78.53% <ø> (+0.49%)	⬆️
snapcraft_legacy/cli/_options.py	85.31% <ø> (ø)
...legacy/internal/pluginhandler/_part_environment.py	87.71% <ø> (+35.08%)	⬆️
snapcraft_legacy/plugins/v2/_kernel_build.py	86.66% <ø> (-11.49%)	⬇️
snapcraft_legacy/plugins/v2/_ros.py	51.61% <27.27%> (-8.11%)	⬇️
...ft_legacy/internal/pluginhandler/_plugin_loader.py	76.04% <75.00%> (-8.31%)	⬇️
... and 34 more

... and 308 files with indirect coverage changes

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