Added Validation of user input for PWM calibration

remove non core parts

Update build_hardware.md

Print message when setting PWM fails.

This prevents the car from completely stopping if there is a weak connection
between the host and the peripheral motor board. Otherwise, a single failed
set_pwm call will halt the host.

fix Hyperlink error

* Simple exception handling to avoid failing

Update index.md

fix typo

Just a simple grammar change for this sentence: "Now your SD card is ready. Eject it from your computer, put it in the Pi, and plug in the Pi."  
- Changed 'you're' to 'your'
- Added a comma after the first Pi.

updated dockerfile

Fix source code of parts directory, to follow PEP8 rules

Fixed conda install path

Update install_software.md

Update install_software.md

The conda install path was pointing to `envs/mac.yml`, but nowhere before that instruction does it tell the reader to `cd` into the `install` subdirectory first, so for the command to work, `install` must be prepended to the path.