Documentation: Add JaCoCo run procedure to Android tools' README.md files

[BukunmiOla]

Writing tests for tools is important, It's also quite important to be able to verify the test coverage in order to keep track of the covered and uncovered components of the tools.
We employ JaCoCo to report test coverage and the dependency has already been added to grade-config.
However, contributors may find it difficult to grasp from the get-go.
Adding this information to the README.md file gives contributors first-hand information about JaCoCo integration with projects and how to generate test coverage reports with JaCoCo.

[BukunmiOla]

@nuilewis, remember the suggestion about adding JaCoCo to projects that does not have it today. I later found out it was added through the gradle-config project. Hence, this issue.