Write documentation for FleXR

[jheo4]

• [x] Setup Doxygen
• [x] Generate code docs with comments
• [x] Setup project page with generated docs
• [ ] General instructions on the webpage
• [x] Setup containers for deployment

[jheo4]

Need to write the Wiki page for Kernel developer / Deployers: how to use FleXR and work on it. Need to polish the main readme