Reword the bootstrap entry and note the macOS paths

README.md, "Entrypoints": the `script/bootstrap` item now says in two
sentences that Go is installed when the machine has none, and that
prettier is installed for the Markdown, with node and yarn when they
are missing.

README.md, the paragraph after the getting-started block: it now says
the block uses macOS paths and that another system puts the destination
in a directory of its own.

Model: fable-5-1

README.md

@@ -91,9 +91,10 @@ vaultik snapshot create
 vaultik snapshot list
 ```
 
-The default config backs up your home directory, with a list of excludes. On
-macOS it also backs up `/Applications`. A configured path that does not exist
-stops the backup, unless you give `--skip-errors`.
+The block uses macOS paths. On another system, put the destination in a
+directory of your own. The default config backs up your home directory, with a
+list of excludes. On macOS it also backs up `/Applications`. A configured path
+that does not exist stops the backup, unless you give `--skip-errors`.
 
 On macOS, grant your terminal app Full Disk Access before the first backup. The
 setting is under System Settings, Privacy & Security, Full Disk Access. Without
@@ -1338,8 +1339,8 @@ 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 node, yarn and prettier for
-  the Markdown. It fails without Docker.
+  `script/install-go` when the machine has none. It installs prettier for the
+  Markdown, and node and yarn when they are missing. It fails without Docker.
 - `script/setup`: prepares a fresh clone. It runs `script/bootstrap` and
   `script/install-precommit`.
 - `script/test`: runs the whole test suite, by building the `test` stage of the