Modified the file to remove the old method of downloading the conatiner and added the singularity website for ease of acccess.

	modified:   README.md

- should conflict with another MR

- Took out gatsby template README contents.
- Put dummy text. Needs more detail.

	modified:   part3/simulating_detectors.md

	modified:   src/@rocketseat/gatsby-theme-docs/styles/theme.js
	modified:   src/docs/part3/simulating_detectors.md

	new file:   src/@rocketseat/gatsby-theme-docs/components/Docs/EditGithub.js

	modified:   part2/adding_detectors.md
	new file:   part3/simulating_detectors.md
	new file:   part4/sensitive_detector.md

	modified:   getting-started/quickstart.mdx

	modified:   ../../static/example_cell_size.png

	modified:   ../../static/DD4hep_block_diagram.svg
	new file:   ../../static/DD4hep_block_diagram2.svg
	new file:   ../../static/dd4hep_DetElement.png

	new file:   ../../static/data_model_use2.png
	new file:   ../../static/example_cell_size.png
	new file:   ../../static/example_digi.png

	modified:   part1/simple_detector.md

	new file:   overview.md
	renamed:    gettingstartedold.mdx -> usage/gettingstartedold.mdx
	new file:   usage/introduction.mdx

	new file:   DD4hep_block_diagram.svg
	new file:   LDRD_EIC_proposal_diagram.pdf
	new file:   LDRD_EIC_proposal_diagram.svg
	new file:   data_model_use.png
	new file:   talks/Argonne_EIC_software_ESC_March_2017.pdf
	new file:   talks/BNL_meeting_10-17-2016.pdf
	new file:   talks/ESC_Oct2017.pdf
	new file:   talks/ESC_meeting_8-4-2016.pdf