Add build instructions to the README

[asfimport]

Need to add instructions to the README for building parquet-thrift and parquet-protobuf. Basically copy what we have Travis CI do in .travis.yml.

Reporter: Ryan Blue / @rdblue
Assignee: Ryan Blue / @rdblue

Related issues:

• Release parquet-mr 1.6.0 (blocks)

PRs and other links:

• PR #156

_{Note: This issue was originally created as PARQUET-230. Please see the migration documentation for further details.}

[asfimport]

Ryan Blue / @rdblue:
Fixed in PR #156.