Ignore flake.lock and explain why

Reflect the previous commit in the readme

Solve layers of indirection problem with /run/current-system/sw/bin

Bubblewrap is adding a new --argv0 option. This means that the command
name can remain unchanged, while the exe to execute can have realpath
applied to it.

Test-1: nix-bwrap date    # coreutils provided on NixOS
Test-2: nix-bwrap find /  # /run/current-system/sw/bin/find on NixOS

Note that --argv0 was only merged into bubblewrap today and there has not
been an offical release. See:
https://github.com/containers/bubblewrap/issues/91

Parse `DISPLAY` variables that include a screen number

The `DISPLAY` environment variable may optionally also
include a screen number after the display number: `:0.0`.

This change makes sure the display number is correctly
extracted even in this case.

Give some examples of errors that indicate missing flags

Perhaps trivial, but may save some confusion for newcomers

Revert "Add defaultPackage"

This reverts commit 767223a7e33e14e119bee3d8c3884ea39cc0587e.

Add defaultPackage

readme: don't dump nixpkgs into scope

closureInfo

Add wrappers

Add note about writeReferencesToFile

Add note about absent nix runtime input

Fix typo

Fix NixOS detection

Mention -help in the readme

Consistent capitalization in help

Set $XDG_RUNTIME_DIR when -pulse is used

If it's unset, pactl errors out:
Connection failure: Connection refused
pa_context_connect() failed: Connection refused

Fixes: https://todo.sr.ht/~fgaz/nix-bubblewrap/1

Use nix profiles for extra-store-paths

Add them to $PATH too

Write to stderr where appropriate

Implement extra-store-paths