(docs) Update README to remove reference to lerna run build

[ibacher]

Requirements

• This PR has a title that briefly describes the work done, including the ticket number if there is a ticket.

For changes to apps

• My work conforms to the OpenMRS 3.0 Styleguide.

If applicable

• My work includes tests or is validated by existing tests.
• I have updated the esm-framework mock to reflect any API changes I have made.

Summary

Just a documentation change. I missed this in my initial PR for turbo support. yarn build should be a stable command that calls whatever build tool we're using.

Screenshots

Related Issue

Other

[github-actions]

File size impact

Merging turbo-update-readme into master impact files as follow:

@openmrs/esm-devtools-app (no impact)

Files	new size
Unmodified (5)	483 kB (0 B / +0%)	👻
Total (5)	483 kB (0 B / +0%)	👻

@openmrs/esm-implementer-tools-app (no impact)

Files	new size
Unmodified (22)	2.44 MB (0 B / +0%)	👻
Total (22)	2.44 MB (0 B / +0%)	👻

@openmrs/esm-login-app (no impact)

Files	new size
Unmodified (29)	2.09 MB (0 B / +0%)	👻
Total (29)	2.09 MB (0 B / +0%)	👻

@openmrs/esm-offline-tools-app (no impact)

Files	new size
Unmodified (27)	2.84 MB (0 B / +0%)	👻
Total (27)	2.84 MB (0 B / +0%)	👻

@openmrs/esm-primary-navigation-app (no impact)

Files	new size
Unmodified (18)	2.26 MB (0 B / +0%)	👻
Total (18)	2.26 MB (0 B / +0%)	👻

@openmrs/esm-app-shell (no impact)

Files	new size
Unmodified (4)	2.19 MB (0 B / +0%)	👻
Total (4)	2.19 MB (0 B / +0%)	👻

_{Generated by @jsenv/file-size-impact during Report bundle size#2156770929 on 0a62bd2}