Add LICENSE, update .gitignore, add security note to README

- MIT LICENSE (2026 Thales Maciel)
- .gitignore: replace broad /build/ with explicit /build/bin/ and
  build/manual/ so large manual rootfs/kernel artifacts are clearly
  excluded; add *.pem, *.key, id_rsa
- README: add Security section documenting intentional
  PermitRootLogin yes / StrictModes no in guest sshd and the
  network boundary that makes it acceptable

.gitignore

@@ -1,5 +1,6 @@
 state/
-/build/
+/build/bin/
+build/manual/
 /runtime/
 /dist/
 /banger
@@ -12,3 +13,6 @@ state/
 squashfs-root/
 rootfs*
 wtf/*.deb
+*.pem
+*.key
+id_rsa

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Thales Maciel <thales@thalesmaciel.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -280,6 +280,21 @@ Alpine support currently applies to the explicit register-and-run flow above.
 The generic `banger image build --from-image ...` path remains Debian/systemd-
 oriented and should not be treated as an Alpine image builder.
 
+## Security
+
+Guest VMs are single-user development sandboxes, not multi-tenant servers.
+Every provisioned image is configured with:
+
+```
+PermitRootLogin yes
+StrictModes no
+```
+
+This is intentional. The host SSH key is the only authentication mechanism,
+no password auth is enabled, and VMs are reachable only through the host
+bridge network (`172.16.0.0/24` by default). Do not expose the bridge
+interface or the VM guest IPs to an untrusted network.
+
 ## Notes
 
 - Firecracker is resolved from `PATH` by default.