fix: ignores always overwritten doc builtin file and fixes wrong formatting at generating doc builtin file
1. Fix
The file at manual/src/builtins.md is always overwritten by this make file section
2. Fix
Before this PR the locally generated builtin doc file looks like this:
After the fix by this PR it looks like this
About CI
The job linux:stable of the CI of Ion fails with compiling error.
See this issue for more details.