Write section about software naming in Application Updates chapter

Acceptance criteria:

• Modify the "Artifact-creation/Application-Updates" chapter (doesn't exist at the time of writing this, see [blocked task|MEN-3218])
• Write how to use --software-name to track names of certain pieces of software. Typical use case:
  • User wants to install his own app "myapp"
  • When creating artifacts containing this app, he uses --software-name myapp
• Write how to use --software-version to track the version of such software
• Write how to --software-filesystem to track applications that are on other partitions than on the rootfs.
• Explain the differences between artifact name, software name and software version

Feature branch name: feature-partial_updates