hs-64 tutorial edits

[ChucklesOnGitHub]

• the tutorial contains auxiliary data but those channels are not physically linked to anything on the headstage
• the imu axes are wrong, should be 0, -1, 0 for proper operation

[cjsha]

@jonnew was just explaining to me how the e-stim signal can be read back through the aux data. This will be included in the hardware guide

the imu axes have been fixed, and that fix has been deployed.