Updated graphics from C5 to C7 and updated Readme.md to showcase updated BeagleConnect Freedom board.

Update zephyr build instructions 

More TODO: to WARNING: TODO

* Change TODO: to WARNING: TODO 
* Note some desired changes, like removing install of bb-code-server and having it be default

New Graphics for BCF C5

BeagleConnect pinout spreadsheet for easy reference.

Updated the back image.

Buttons are added.

Annotated image shows pinout for beagleconnect back side.

Annotated image shows pinout for beagleconnect front side.

New presentation image for BeagleConnect Freedom Rev C5.

New BCF block diagram has been added for Rev C5.

New datasheets has been added for the sensors onboard and CC1352P. All the datasheets are now in one folder.

WIP

Help make it a bit clearer what modes the LEDs indicate.

System Reference Manual 

Instructions are added to install bb-code-server on BeagleBone green gateway to easily access the terminal and edit code.

These images/screenshots shows the bb-code-server running on Beaglebone green Gateway device.

This is the rendered System Reference Manual (SRM) for BeagleConnect™ which still requires a lots of edits and improvements.

This is used to make the HTML & PDF look pretty :)

This page provides introduction to the thoughts behind creating BeagleConnect™

this page will help with indexing for SRM

In this chapter we take a look at greybus stack for BeagleConnect™