refactor: Move external storage file name encoding to external storage chapter

[joshtrichards]

☑️ Resolves

The "file name encoding" section was the only External Storage topic in the fairly buried general Troubleshooting chapter.

Moved it to the External Storage chapter where it's more obvious and logical to look for it. Also it's arguably a configuration matter anyhow.

Also very lightly touched up the main External Storage chapter: headings, grammar, etc.

🖼️ Screenshots