Write Tool chain Sum-up Document

[cecilebraun]

The tool chain architecture document will give a status on the tool chain and give some hints and advice for the next openETCS tool chain generation.
https://github.com/openETCS/toolchain/blob/master/T7.3/ToolChainArchitecture/WP7-Toolchain_architecture.pdf.
@openETCS/toolchain-committer need to complete this document.

• Chapter 2 describes the status of the tool chain
  • This chapter has to be checked
  • Feature or plugin missing should be added in the figures
• Chapter 3 describes the activities contains in the toolchain
  • For each plugin we need a small description and a link to the documentation
• Chapter 4 is about how to test the tool chain
  • Complete the list of requirements
  • Give the link to the test plan and the tests specification
• Chapter 5 sum up what is implemented inside the tool chain
  *[ ] A table should be filled for each Feature/plugin