[SPARK-11963][DOC] Add docs for QuantileDiscretizer

[yinxusen]

https://issues.apache.org/jira/browse/SPARK-11963

[SparkQA]

Test build #46673 has finished for PR 9962 at commit b054a54.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * public class JavaQuantileDiscretizerExample\n

[jkbradley]

I'll review now

[jkbradley]

In the last instance, this uses 2.2, but your Markdown example uses 22. This must be the cause of the buckets being out-of-order in the example.

[jkbradley]

That's the only issue I see.

[yinxusen]

Thanks @jkbradley, it's my fault. I tested both JavaQuantileDiscretizer and QuantileDiscretizer just now. Given the 4th row 2.2, we get the result showed in the doc, other than 22.0. So I changed the 22.0 -> 2.2 in both ml-features and JavaQuantileDiscretizerExample.

[SparkQA]

Test build #47106 has finished for PR 9962 at commit fede71b.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * public class JavaQuantileDiscretizerExample\n

[BenFradet]

"may be different" or "may differ" but not "may different"

[BenFradet]

There is a typo but otherwise it looks good.

[yinxusen]

Thanks @BenFradet for the comments. I fixed them.

[SparkQA]

Test build #47180 has finished for PR 9962 at commit 17655aa.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * public class JavaQuantileDiscretizerExample\n

[jkbradley]

Thanks! I'll test once more and then merge

[SparkQA]

Test build #2176 has finished for PR 9962 at commit 17655aa.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * public class JavaQuantileDiscretizerExample\n

[jkbradley]

LGTM, merging with master and branch-1.6