Add README for ext/mysqli tests

[tiffany-taylor]

I created a readme file to explain what's necessary to run the ext/mysqli tests. I used the pdo_mysql README as a rough example to write this.

I'm unsure if the statement

The MySQL user used to run the tests must have full permissions on the test database.

is accurate with ext/mysqli. I'm guessing that the statement is correct, given that a database and test user are required to run the tests. If I'm wrong, please correct me.

[Girgias]

Maybe it would be nice to provide the command to create the test DB:
mysql -u root -e "CREATE DATABASE test"

[tiffany-taylor]

Maybe it would be nice to provide the command to create the test DB:
mysql -u root -e "CREATE DATABASE test"

I would think that would be assumed, but that also assumes the person has an understanding of MySQL at the outset. I can add instructions on what's needed for setup, if that is desired.

[Girgias]

Maybe it would be nice to provide the command to create the test DB:
mysql -u root -e "CREATE DATABASE test"

I would think that would be assumed, but that also assumes the person has an understanding of MySQL at the outset. I can add instructions on what's needed for setup, if that is desired.

I don't know how all databases work and what their CLI interface are, thus I think it would be a nice addition, maybe also a mention that the tables needed to run the tests are created and torn down by the test suite just to prevent someone from creating a dedicated table in the database.

[tiffany-taylor]

It might be a good idea to add similar instructions to the pdo_mysql README as well...

[tiffany-taylor]

@Girgias how does this sound?

Forgot to add an explanation about creating a dedicated table, which is now included in the latest commit.

[Girgias]

LGTM

[cmb69]

Thanks!