Update README.md

[mirnawong1]

this pr adds an intro to dbt core as well as bullets for the diff ways to deploy dbt. this stemmed from task last year: https://www.notion.so/dbtlabs/Mirna-will-review-cloud-cli-repo-per-Greg-s-request-0a372ebb66794a749350b0fbb36ee266?pvs=4

Problem

currently its not clear the ways to deploy dbt, this pr tries to clarify that a little.

Solution

Checklist

• [ x] I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• [x ] This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.78%. Comparing base (71a8a41) to head (45bbaf6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10324      +/-   ##
==========================================
- Coverage   88.83%   88.78%   -0.06%     
==========================================
  Files         180      180              
  Lines       22490    22490              
==========================================
- Hits        19980    19967      -13     
- Misses       2510     2523      +13     

Flag	Coverage Δ
integration	86.04% <ø> (-0.15%)	⬇️
unit	62.19% <ø> (ø)

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