chore: Simulator Docker instructions

diff --git a/.gitignore b/.gitignore
index ed8510c..0623e03 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,3 +26,4 @@ __pycache__/
 pp
 
 .idea/
+firmware
\ No newline at end of file
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..35ffc5a
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,32 @@
+FROM gcc:11.5.0-bullseye
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get update && apt-get install -y \
+    git \
+    make \
+    python3 python3-venv python3-pip \
+    swig \
+    libpcsclite-dev pcscd \
+    pkg-config \
+    libffi-dev \
+    xterm \
+    autoconf automake libtool m4 
+
+WORKDIR /build
+
+RUN git clone --depth 1 --recursive \
+    https://github.com/Coldcard/firmware.git
+
+WORKDIR /build/firmware/unix
+
+# Build mpy-cross
+RUN make -C ../external/micropython/mpy-cross
+
+# Build simulator & tools
+RUN make setup
+RUN make ngu-setup
+RUN make
+
+# remove unnecessary git files
+RUN find /build/firmware -name ".git" -type d -prune -exec rm -rf '{}' +
\ No newline at end of file
diff --git a/README.md b/README.md
index e0cbbb7..1e5a9e0 100644
--- a/README.md
+++ b/README.md
@@ -91,6 +91,25 @@ so at the top level, do this command:
 pip install -r requirements.txt
 ```
 
+### Using Docker to build simulator
+Install [Docker Desktop or Docker Engine](https://docs.docker.com/desktop/) (don't forget to add your user to the docker group `sudo usermod -aG docker $USER` than logout and login again)
+
+```
+# Build simulator
+docker build -t coldcard-simulator .
+docker create --name cc coldcard-simulator
+docker cp cc:/build/firmware ./firmware
+docker rm cc
+
+# Install specific libffi7 (as new Ubuntu versions ship with libffi8 only)
+wget http://archive.ubuntu.com/ubuntu/pool/main/libf/libffi/libffi7_3.3-4_amd64.deb
+sudo dpkg -i libffi7_3.3-4_amd64.deb   
+
+# Run simulator (remember to follow the OS specific instructions detailed below to install python and its dependencies)
+cd firmware/unix
+./simulator.py
+```
+
 ### macOS
 
 [Python 3.5 or higher](https://www.python.org) and [Homebrew](https://brew.sh) is required.
@@ -179,7 +198,13 @@ All steps you need to install and run the Coldcard simulator on Ubuntu 20.04:
 apt install build-essential git python3 python3-pip libudev-dev gcc-arm-none-eabi libffi-dev xterm swig libpcsclite-dev python-is-python3 autoconf libtool python3-venv
 
 # Get sources, this takes a long time (because of external libraries), then open
+
+# Recommended (fast, minimal download; sufficient for building and running the simulator):
+git clone --depth 1 --recursive https://github.com/Coldcard/firmware.git
+
+# Full clone (developers only; required for history, bisecting, or contributing):
 git clone --recursive https://github.com/Coldcard/firmware.git
+
 cd firmware
 
 # Apply address patch
diff --git a/unix/simulator.py b/unix/simulator.py
index af7e94f..9840eb1 100755
--- a/unix/simulator.py
+++ b/unix/simulator.py
@@ -903,8 +903,14 @@ Q1 specials:
         child.kill()
         return
 
+    logfile = '/tmp/cc_simulator.log'
+
+    # truncate logfile and set correct permissions before starting xterm
+    open(logfile, 'w').close()
+    os.chmod(logfile, 0o644)
+
     xterm = subprocess.Popen(['xterm', '-title', 'Coldcard Simulator REPL',
-                                '-geom', '132x40+650+40', '-e'] + cc_cmd,
+                                '-geom', '132x40+650+40', '-l', '-lf', logfile, '-e'] + cc_cmd,
                                 env=env,
                                 stdin=subprocess.DEVNULL, stdout=subprocess.DEVNULL,
                                 pass_fds=pass_fds, shell=False)