Clarify "used" in https://forensics.wiki/fileobject/

[joachimmetz]

https://forensics.wiki/fileobject/ states:

Not sure what this means.

Which refers to the <used> tag

Also the formatting of the table in in the page seems to be off.

[joachimmetz]

Some changes in #246

[joachimmetz]

Additional changes to make after merge:

• clarify <used> tag - https://github.com/dfxml-working-group/dfxml_schema/blob/a80a8619d83ac23c7cd41bd9262be86fcebe3bd8/dfxml.xsd#L713
• add reference to https://simson.net/ref/2011/dfxml.pdf
• mention known shortcomings of the format Require DFXML be encoded as UTF-8 dfxml-working-group/dfxml_schema#34 and Clarify: "NTFS's "Inode" numbers are the MFT entry address." dfxml-working-group/dfxml_schema#45