Update CHANGELOG.md
Update CHANGELOG.md

Explain changes in gains units.
madcowswe/ODriveFirmware,madcowswe/ODrive,madcowswe/ODrive,madcowswe/ODrive,madcowswe/ODriveFirmware,madcowswe/ODriveFirmware,madcowswe/ODrive,madcowswe/ODrive,madcowswe/ODriveFirmware