Update README.md

Link sub projects, update common-tool to cmake-tool, and add a link to
the CONTRIBUTING.md file.

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

github setup for CoC, License, Contributing

This commits adds links to the seL4 code of conduct (COC) and
contribution guidelines to the github setup. It also moves the license
remarks to its owns LICENSE.md file that is recognised by github.

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

convert license headers to SPDX

Includes license review of 3rd-party files, adding missing upstream
headers, and moving the UNSW OZPLB license into its own file rather
than replicating it in the header.

trivial: remove out of date README comments

trivial: update README to escape _

README: add dts

Fix whitespace

- remove trailing whitespace
- remove duplicate blank lines
- remove blank lines at end of file

Fix licenses

Add a tool for determining provenance of code forked from an upstream repo.

This adds a tool that is a quick and dirty implementation I wanted in order to
find the upstream Linux commit we forked Kconfig from. It could easily be
improved in future with obvious optimisations (e.g. fetch upstream into the same
working directory and use git-diff instead of diff) if necessary.

Add LICENSE_GPLv2 to KBuild, update readme

Initial commit