Update README.md and manifest.txt

[pablgonz]

Hi, the file README.md needs a bit of updating:

• 3ed, https://github.com/latex3/latex2e/blob/a8e84e99aa3be6d206cc90494cd10e6a8c300dda/base/README.md?plain=1#L32
• add tlc3.err. https://github.com/latex3/latex2e/blob/a8e84e99aa3be6d206cc90494cd10e6a8c300dda/base/README.md?plain=1#L59
• 1989 -204, https://github.com/latex3/latex2e/blob/a8e84e99aa3be6d206cc90494cd10e6a8c300dda/base/README.md?plain=1#L90

The file manifest.txt missing ltnews38 and ltnews39.

Brief outline of the bug

Minimal example showing the bug

\RequirePackage{latexbug}       % <--should be always the first line (see CONTRIBUTING)!
\documentclass{article}

  % Any preamble code goes here

\begin{document}

  % Demonstration of issue here

\end{document}

Log file (required) and possibly PDF file