Add instructions for correct player version insertion

[defagos]

• As an SRG SSR analyst I want the player version to be correctly reported in comScore and Commanders Act payloads sent from apps integrating Pillarbox.
• As a Pillarbox developer I want the player version to be correctly reported in monitoring events sent from apps integrating Pillarbox.
• As a developer integrating Pillarbox I want correct instructions how to setup my project so that these needs can be guaranteed.

Context

We discovered that recently released SRF apps did not send player version information. Since the player version is extracted by a plugin performing a git blame we easily pinpointed this issue to be related to how the SRF apps are distributed, in particular the fact that their delivery workflow was restoring an SPM cache with possibly missing tags.

Acceptance criteria

• Improve documentation to mention issues related to the use of cached SPM packages in release workflows (always use clean build).

Tasks

• Document the above.