Fix links to content on the new version of zephyrproject.org that moved.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

This patch adds information about the security related issue
tracking.

Signed-off-by: Andy Gross <andy.gross@linaro.org>

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

Zephyr Security WG requests listing a point of contact on the main
GitHub repo README for security-related inquiries. (This section of
the README is also included in the project intro page, via include
directive.)

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

LF is requesting a Core Infrastructure Initiative evaluation
and badge on our website.  This PR introduces that into our
README.rst on GitHub and also merges content from the
README into our introduction document.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

More general spelling fixes, and cleaning up stray UTF-8 characters
such as curly-quotes, em- and en-dashes.  Use replacement strings
for |reg| and |trade|.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

github doesn't handle sphinx directves (and ends up displaying them)

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

Jira: ZEP-2055

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>