Update README.md

Updated README to mention what policy needs to be removed to allow for datastream version deletion.
stack on ingest
cleaner watchdog
ingest form watchdog
Merge pull request #417 from willtp87/7.x.better_errors

7.x.better errors
object ingest success message
add filter xss
forgot add this file
convert to the right version
Merge pull request #419 from willtp87/7.x.better_errors

object ingest success message
Merge branch '7.x' of https://github.com/Islandora/islandora into 7.x-add-xss
convert to islandora 7.x
recover islandora 7.x
recover islandora 7.x
add xss filter to the title
Merge pull request #420 from yqjiang/7.x-add-xss

7.x add xss