doc: remove "note that" from fs doc

Remove "note that" from the fs documentation, along with other minor nearby improvements.

Before:

Note that some characters are obscured by Strong Bad's head.

After:

Some characters are obscured by Strong Bad's head.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines