Extend ENSDb documentation

[tk-o]

Documentation present at https://ensnode.io/ensdb/ needs to be updated to present an overview about ENSDb service, and how to use it. There should be examples for interacting with ENSDb with ENSDb Reader and ENSDb Writer classes from ENSDb SDK.

Here's the current outline I created for the ENSDb Docs:
https://docs.google.com/document/d/1EodQIeotwAHB3bKFsb-Tca17tg7b-Ji6tijJ3yuB_Hk/edit?tab=t.0

[tk-o]

Resolved with #1942