README.md: Restore SQLAlchemy docs and links

The explanation for sqlalchemy_index_database was removed in bb69c43f
(update documentation for config_sample.yml changes, 2014-05-14), and
the reference URL for search-endpoint was removed in 4ba12e5d (Updated
documentation for 0.7, new developer (contribute) doc, new changelog
file, 2014-05-20).

Since I added the links in fab832bf (search: Use SQLAlchemy as a
search-index backend, 2014-02-12), the search-endpoint URL has moved
from:

  http://docs.docker.io/en/latest/reference/api/index_api/#get--v1-search

to:

  http://docs.docker.com/reference/api/docker-io_api/#search

But I haven't tracked down the Docker-side commit responsible for that
move.
docker_registry.index: Remove local logger

This was added in d2ace65d (Naive mirroring implementation,
2014-02-06) in support of some
/v1/repositories/<path:repository>/images logging.  Those logs were
removed in bbb487a3 (Using mirroring decorator on index route,
2014-03-07), but this code was left behind.
Updated run.py to include env variables for logging gunicorn to files
Updated eny.py to include default logging to console / docker logs
Merge pull request #479 from wking/index-logger

docker_registry.index: Remove local logger
Merge pull request #472 from wking/readme-restore-sqlalchemy

README.md: Restore SQLAlchemy docs and links
Merge pull request #481 from Furze/master

Add environment variables for gunicorn logging
fix(logging): move up logging setup
fix yaml escape bug
Merge pull request #487 from deis/fix-yaml-bug

Fix YAML escape bug on Gunicorn log targets
Merge pull request #485 from deis/fix-logging-setup

Configure logging before modules that require it
docker_registry.run: Restore GUNICORN_OPTS functionality

This was initially added in 534c6da5 (run.sh: Add '$GUNICORN_OPTS
"$@"' to gunicorn invocation, 2014-02-13), but didn't survive the
translation to a setuptools entry_points in bf3360a2 (replacing run.sh
with a "docker-registry" console script, 2014-04-02).  bf3360a2 was
part of dotcloud/docker-registry#297, which branched off before
534c6da5 landed with dotcloud/docker-registry#247, and the
entry_points invocation wasn't updated to reflect the change.

The syntax has also changed a bit, since we're invoking Gunicorn from
Python instead of Bash.  Instead of dropping the string verbatim onto
the command-line ($GUNICORN_OPTS), it now goes through the usual
docker_registry.server.env.source YAML parsing (884b418f, Type from
environment properly (like Config), 2014-06-23).  So instead of
something like:

  GUNICORN_OPTS='--preload --log-syslog'

you should now be using:

  GUNICORN_OPTS='[--preload, --log-syslog]'