fix: Fixed example materialize-incremental and improved explanation

[dandawg]

What this PR does / why we need it:

In the quickstart documentation, step 6 mistakenly provides both start and end date parameters to the feast materialize-incremental command (which only takes an end date). This was probably just confused with the parameters for the feast materialize command. Running the command as is results in an error.

In addition, the docs explain that materialize-incremental "serializes all new features since the last materialize call", but this is confusing since no materialize call has been run in the quickstart.

In this PR, I fixed the parameter input, and improved the documentation to include a mention of when the ttl is used.

Which issue(s) this PR fixes:

Misc

To reproduce the issue:

1. Initialize the quickstart repo: feast init feature_repo # run in examples/quickstart
2. Apply the repo config: feast apply
3. Try running the command from step 6 in the quickstart documentation:

   
   LAST_YEAR=$(date -u -v -1y +"%Y-%m-%dT%H:%M:%S")

feast materialize-incremental $LAST_YEAR $CURRENT_TIME

Error Output:

```feast materialize-incremental $LAST_YEAR $CURRENT_TIME
Usage: feast materialize-incremental [OPTIONS] END_TS
Try 'feast materialize-incremental --help' for help.

Error: Got unexpected extra argument (2024-11-04T17:42:12)