Links in usage doc lead to 404's

[alohr51]

Links under Usage header in https://github.com/IBM/carbon-icons/blob/master/docs/usage.md lead me to 404's, here are some examples:

• https://github.com/carbon-design-system/carbon-icons/tree/master/dist
• https://raw.githubusercontent.com/carbon-design-system/carbon-icons/master/dist/carbon-icons.svg
• http://carbondesignsystem.com/style/iconography/library

[joshblack]

Thanks for the heads up @alohr51! Updating now 👍