Correct README.md on where warnings go and on which make targets use Docker and script/

Warnings and the per-file errors of `snapshot restore` are written to stdout
through `internal/ui`, so the stdout list names them and the redirect example
says a file captures them. Only `make test` and `make lint` run inside Docker;
`make test-coverage` runs on the host. Some `Makefile` targets (`build`,
`clean`, `deps`, `test-coverage`, `local`, `install`) call no `script/` entry,
so "Most" replaces "only".

Fixes the two findings of the fourth review of
#399.

Model: fable-5-1

README.md

@@ -1084,6 +1084,7 @@ No other command takes the lock. `snapshot list`, `snapshot verify`,
 stdout carries the output you asked for:
 
 - status and progress lines
+- warnings, and the errors that `snapshot restore` prints about files
 - tables and reports
 - JSON documents
 - `config get` values
@@ -1095,8 +1096,8 @@ stderr carries the rest:
 - log records, including those from `--verbose` and `--debug`
 - the error that a failed command ends with
 
-So `vaultik snapshot list > out.txt` captures the list and leaves the
-diagnostics on your terminal.
+So `vaultik snapshot list > out.txt` captures the list and any warnings. The
+banner, log records and a final error stay on your terminal.
 
 Log records are colored lines when stderr is a terminal. They are JSON, one
 object per line, when stderr is redirected.
@@ -1223,8 +1224,8 @@ Two documents give the rules for work on this repository:
 ### Requirements
 
 - Go 1.26.1 or later.
-- Docker, with a daemon you can reach. The tests and the linter run only inside
-  Docker.
+- Docker, with a daemon you can reach. `make test` and `make lint` run inside
+  it.
 
 ### Workflow
 
@@ -1240,8 +1241,8 @@ pass.
 
 This repository follows the
 [Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
-standard. The scripts in `script/` are the entrypoints. The `Makefile` targets
-only call them.
+standard. The scripts in `script/` are the entrypoints. Most `Makefile` targets
+call them.
 
 - `script/bootstrap`: installs what development needs. It installs Go from
   `script/install-go` when the machine has none, and it fails without Docker.