docs: --target becomes --filter

[talss89]

@mikespainhower on Discord pointed out that --target seems to have been removed.

It looks like to me that the same functionality is now provided by --filter. Have tested --filter on a multi-instance setup and it targets the instance with the matching bud.context.label.

This PR is a search-replace on the docs page, --target becomes --filter.

Still haven't got a working Bud-dev setup running, so these will need compiling too (sorry).

Type of change

NONE: internal change

[kellymears]

Thank you!

In this case there was no need to run yarn @bud docs since the generated README.md contents didn't change.

Despite that, the root README.md had (unrelated) fixes waiting to be applied (whoops), so I ran the command anyway.

I also manually deployed this change (yarn @bud netlify deploy, but I'm the only one with credentials for deploying the docs because netlify is priced per seat and actually kinda expensive..)

The test failure was random -- sometimes e2e can be a bit flaky.