Fix minor "substityte" typo in OCIO Branding guide

[mrjschulte]

There is a minor typo in the opencolorio-branding-guide.pdf.

On page 4 showing how to NOT use the branding elements there is a sentence that reads "don’t substityte with type or modify".

This should read "don’t substitute with type or modify"

[mrjschulte]

@jmertic for insights...

[jmertic]

Thanks @mrjschulte !

@carolalynn22 Can you review? I believe the project produced this.