fix(docs): add base to og image using env variable

mentioned in commit 9c562c78

mentioned in commit cfe88602

mentioned in commit 6f8d073a

mentioned in commit 3ee6dd49

mentioned in commit f066b7b5

mentioned in commit d54a8ce8

mentioned in commit 0eeedb9d

mentioned in issue #499 (closed)

mentioned in commit f07f561c