Update OTB readme and deadlinks

Description

For the next OTB 10, update the link in the readme and other otb pages that are dead or outdated:

• make a pass on the readme
• check all other markdown files
• check the rst files
• check the website

Definition of Ready

Generic:

• If this issue is consequent, it is splitted in sub-tasks with priority and complexity evaluated. Theses sub-tasks should be linked to this issue. (To do on gitlab interface after writing this issue)
• Issue complexity evaluated
• Priority of issue evaluated
• If there is specific test data needed, it should be detailed and available
• If there is specific documentation/specification need, it should be available to the development team
• Time during the sprint to realize this issue
• Blocking elements resolved (check if non applicable, detail otherwise the resolved elements)

Specific:

Definition of Done

Specific

• all markdown files correctly displayed in gitlab
• no more deadlinks