[JAVA] Document requirements and non/requirements for ValueVector updates

[asfimport]

Requirements Document https://docs.google.com/document/d/1ysZ76zritBDwkeQz3C6-vhQwD32jEXd1kUF4T936G1U/edit

Reporter: Jacques Nadeau / @jacques-n
Assignee: Siddharth Teotia / @siddharthteotia

_{Note: This issue was originally created as ARROW-1471. Please see the migration documentation for further details.}

[asfimport]

Siddharth Teotia / @siddharthteotia:
Planning to start a doc today to pen-down all the requirements. Will circulate for review thereafter.

[asfimport]

Siddharth Teotia / @siddharthteotia:
We have an agreement and understanding of the requirements. Have received feedback from the community.