Improves the documentation on how to configure build.rs

[patmuk]

Changes

Fixes #1742

Checklist

• An issue to be fixed by this PR is listed above.
• New tests are added to ensure new features are working. Please refer to this page to see how to add a test.
• ./frb_internal precommit --mode slow (or fast) is run (it internal runs code generator, does auto formatting, etc).
• If this PR adds/changes features, documentations (in the ./website folder) are updated.
• CI is passing. Please refer to this page to see how to solve a failed CI.

@fzyzcjy please not that I took the liberty to change the md-file to have one sentence per line. In this way, future changes are easier to see in the diff. The output should not be affected by this reformatting.

Probably my description is a bit to verbose - feel free to reformulate or ask me to do so!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f221ce8) 99.27% compared to head (26550cb) 99.25%.

❗ Current head 26550cb differs from pull request most recent head a56e856. Consider uploading reports for the commit a56e856 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1743      +/-   ##
==========================================
- Coverage   99.27%   99.25%   -0.02%     
==========================================
  Files         357      357              
  Lines       14813    14813              
==========================================
- Hits        14705    14703       -2     
- Misses        108      110       +2     

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[patmuk]

@fzyzcjy I guess all is fine (except for you to have an editorial look upon the proposed reformulation).
The CI fails two tasks:

1. Code coverage shrank -> not sure why, as even the report states that no file changed. I accidentally used a wrong comment sign in the cargo.toml, and fixed that - so maybe it complains about introducing and then removing a line. Though the report compares master with the last commit in this branch.
2. frb_example/flutter_via_create fails. I did not changed anything there, maybe a flaky run?

[fzyzcjy]

Code coverage shrank, frb_example/flutter_via_create fails

Just flaky, no worries!

[patmuk]

@fzyzcjy thanks for the corrections!

[fzyzcjy]

You are welcome!