pin tf to 1.13.1

Update setup_raspberry_pi.md

Update build_hardware.md

Updated precompiled cv2 instruction for JetPack 4.3

Fix minor typo.

For rPi 4B and Jetson Nano processor boards the higher power comes at a price of higher input power and since the voltage remains the same( 5V ) the current must increase. So it's recommended you get a USB battery pack with 3A output capabilities or higher.

* Updated filepath
* Added Numpy install command (pip install numpy failed, apt-get worked)
* Added hyperlink to skip to next section
* Moved common swap space instructions to the beginning of the section
* Punctuation

Update train_autopilot.md

Update roll_your_own.md

Update setup_raspberry_pi.md

Update setup_raspberry_pi.md

Update images.

Update stores.md

Update about.md

Update simulator.md

Update setup_raspberry_pi.md

Fixed some typos in build_hardware.md

Add section to move model from host  back to the car, add more details about preparing car for automatic driving.

Add URLs to markku.ai project

Fixes #493

added link for finding WiFi configuration file "country" codes.

Replace hand drawn image with a render.
Use lowercase extensions for images.

Add URL to rosbags.

Fix typos.

* ensure docs guide how to handle SD card in a safe way
* make formatting more consistent
* ensure headers about optional steps are easier to spot
* add more details about setting up hostname and discovering IP of the device
* minor fixes

Update setup_mac.md

Update setup_ubuntu.md

Update setup_windows.md

Clarification on what hardware tensorflow-gpu operates

Clarification on when to install tensorflow-gpu

Clarification on when to install tensorflow-gpu