Write test/README.md to help working with tests

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

test/README.md

+Running tests
+-------------
+
+To run all the tests, you may run `make check` under `test/`.
+
+For more control, you may use the `prove` command, which receives a directory
+or a list of files to run, and produces a report.
+
+Each test script is standalone, so you may run them individually. Some tests
+may receive command-line options to help debugging. See for example sharness's
+documentation for shell test scripts:
+https://github.com/chriscool/sharness/blob/master/README.git
+
+### Dependencies
+
+For all the test to run, the following Arch packages should be installed:
+
+- pyalpm
+- python-alembic
+- python-bleach
+- python-markdown
+- python-pygit2
+- python-sqlalchemy
+- python-srcinfo
+
+Writing tests
+-------------
+
+Test scripts must follow the Test Anything Protocol specification:
+http://testanything.org/tap-specification.html
+
+Tests must support being run from any directory. They may use $0 to determine
+their location. Python scripts should expect aurweb to be installed and
+importable without toying with os.path or PYTHONPATH.
+
+Tests written in shell should use sharness. In general, new tests should be
+consistent with existing tests unless they have a good reason not to.