Add Apache 2.0 license to README.md files in parquet-testing

[asfimport]

parquet-testing files can be used for interop tests in parquet-mr.
However, if it is added as a submodule, then the 3 README.md files fail the license check and hence fail build of parquet-mr.

Reporter: Maya Anderson / @andersonm-ibm
Assignee: Maya Anderson / @andersonm-ibm

Related issues:

• Encryption: Interop and Function test suite for Java version (Dependent)

PRs and other links:

• GitHub Pull Request #12

_{Note: This issue was originally created as PARQUET-1834. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Resolved by PR apache/parquet-testing@bcd9ebc