fix(cli): README does not support package manager being used

[ren-yamanashi]

When initialize project using cdk init -l ts --package-manager <package-manager> command, the README.md should contain the following:

(that when selected pnpm)

* `pnpm build`   compile typescript to js
* `pnpm watch`   watch for changes and compile
* `pnpm test`    perform the jest unit tests

But actually README.md contain following:

* `npm run build`   compile typescript to js
* `npm run watch`   watch for changes and compile
* `npm run test`    perform the jest unit tests

I fixed it in this PR.

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.45%. Comparing base (672ee1c) to head (6b72343).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #989      +/-   ##
==========================================
+ Coverage   87.40%   87.45%   +0.04%     
==========================================
  Files          72       72              
  Lines       10023    10052      +29     
  Branches     1314     1317       +3     
==========================================
+ Hits         8761     8791      +30     
+ Misses       1238     1237       -1     
  Partials       24       24              

Flag	Coverage Δ
suite.unit	87.45% <100.00%> (+0.04%)	⬆️

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