Document adding a new test

[oxr463]

The testsuite needs lots of love, but for now, here are some steps to add a new test.

There are more than one type of test, compiled tests written in c, or shell scripts.

Also, if you take a peek at test/GNUmakefile, you will see some tests are hard-coded in there for some reason.

I recently added test/test-python01.sh, so you can use that one as a proper example.

See also: proot-me/proot#164

[oxr463]

@emilio1625 does this help any?

[emilio1625]

Hey thanks! this helps a lot

[oxr463]

Also, per the release guide,

All shell scripts must pass shellcheck.

If you aren't familiar with shellcheck, then check it out, https://www.shellcheck.net

[oxr463]

Also, you can run the testsuite with V=1 for verbose. That really helps, but it is very verbose..