## What changes were proposed in this pull request?
Add AL2 license to metadata of all .md files.
This seemed to be the tidiest way as it will get ignored by .md renderers and other tools. Attempts to write them as markdown comments revealed that there is no such standard thing.
## How was this patch tested?
Doc build
Closes#24243 from srowen/SPARK-26918.
Authored-by: Sean Owen <sean.owen@databricks.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>
## What changes were proposed in this pull request?
Consistency in style, grammar and removal of extraneous characters.
## How was this patch tested?
Manually as this is a doc change.
Author: Shashwat Anand <me@shashwat.me>
Closes#20436 from ashashwat/SPARK-23174.