Collect upgrade guides

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Crowd:

• https://confluence.atlassian.com/crowd/preparing-for-crowd-5-3-1369637323.html

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For REST: https://bitbucket.org/atlassian/atlassian-rest/src/master/ and then the UPGRADE files

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For web resources: https://bitbucket.org/atlassian/atlassian-plugins-webresource/src/master/UPGRADE_700.md

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Jakarta: https://github.com/atlassian-labs/jakarta-adapters