Add examples to snapshotting document

[royjacobson]

for example, how to load a dump.rdb from redis into dragonfly

[romange]

or how to save snapshot manually from dragonfly.
Here is the example of someone who does not know (he used dpkg to install):
https://discord.com/channels/981533931486724126/1113000451789574195

[Niennienzz]

Currently #58, #88 and #100 are partially already covered by the following:

• https://www.dragonflydb.io/docs/managing-dragonfly/backups
• https://www.dragonflydb.io/docs/migrating-to-dragonfly

I will walk through the doc again making sure issues are 100% covered as desired.

[romange]

Thank you @Niennienzz !

[romange]

Closing as completed