Based on https://github.com/matrix-org/rageshake

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Based on MSC3575

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

In order to avoid confusions between the name of the program itself (BorgBackup and Borg in short) and the backups managed by BorgBackup, the official full name should be preferred where possible, minding capitalization.

- Borg or borg → BorgBackup
- Borg backup(s) → BorgBackup (if it means the program) / backups with BorgBackup (if it means the backups managed by the program)

Based on https://www.borgbackup.org/

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Provoked by https://github.com/mother-of-all-self-hosting/mash-playbook/pull/280

Related to https://etke.cc/news/d3uw4utq4t3_rpxicrrfqqou_ynmptqjgk95pt-3n2s/

Issues and Pull Requests were not migrated to the new
organization/repository, so `matrix-org/synapse/pull` and
`matrix-org/synapse/issues` references were kept as-is.

`matrix-org/synapse-s3-storage-provider` references were also kept,
as that module still continues living under the `matrix-org` organization.

This patch mainly aims to change documentation-related things, not actual
usage in full yet. For polish that, another more comprehensive patch is coming later.