Bootcamp for milvus 2.0-rc4

Updates or New features:

• #574 Write template for issue and PR. (@shiyu22 )
• #580 A document about how to contribute.(@shiyu22 )
• #588 Add DNA Sequence Classification to solution(@jaelgu )
• #598 Add video analysis to solution(@jaelgu )
• #613 Update the script of Benckmark test.(@Bennu-Li )

Issue fixes:

• #610 Document content error of reverse images search (@linchpinlin )