Update link to CLI reference in README.md

[CodeMonkeyLeet]

Description

Update Reference Guide link in README.md to dapr docs website instead of
reference docs removed from this repo in #501.

Issue reference

Please reference the issue this PR will close: #686

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

Merging #687 (04b15cf) into master (27794a8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #687   +/-   ##
=======================================
  Coverage   19.79%   19.79%           
=======================================
  Files          28       28           
  Lines        1364     1364           
=======================================
  Hits          270      270           
  Misses       1061     1061           
  Partials       33       33           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 27794a8...04b15cf. Read the comment docs.