docs(support): added documentation about the support policies of Elgg

fixes: #7581
fix(likes): Uses getDisplayName() instead of assuming the object has value in title property
Merge pull request #7620 from juho-jaakkola/likes_target_title

fix(likes): Uses getDisplayName() instead of assuming the object has value in title property
Merge pull request #7609 from jeabakker/support-policy

docs(support): added documentation about the support policies of Elgg