Update Apple Silicon docs

[geoffrey4444]

Proposed changes

The docs for building spectre on Apple Silicon were out of date. This updates the docs. Along the way, I figured out how to get spectre to build with shared libraries, which the instructions now recommend.

Specific changes:

• Removes instructions to build brigand and libsharp, since these are now bundled with spectre
• Fix missing openblas install in homebrew installation instructions
• Change charm++ instructions to i)built with shared libraries, and ii) build without ROMIO, which we don't use but which doesn't build for me for some reason I couldn't figure out
• Instructions now support building with shared libraries on and python bindings on (before they were off)
• Added a one liner at the end on how to install the python bindings in the user's python environment

Depends on #6036

Upgrade instructions

The instructions for building spectre on Apple Silicon have been updated, including enabling python bindings and building with shared libraries instead of static libraries.

Code review checklist

• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.
• The PR lists upgrade instructions and is labeled bugfix or
  new feature if appropriate.

Further comments

[geoffrey4444]

Thanks very much for taking a look at this, @nilsvu ! Because your changes were all very small one-liners, I squashed immediately. Ready for another look when you get a chance