Add Dockerfile and instructions to build with Docker

.dockerignore

@@ -0,0 +1,3 @@
+.vscode/
+.calc.dSYM/
+.DS_Store

Dockerfile

@@ -0,0 +1,12 @@
+FROM alpine:3.12
+# install gcc, make, libc and the bdw gc
+RUN apk add --no-cache gcc make libc-dev gc-dev
+# install leg
+RUN wget -qO- https://www.piumarta.com/software/peg/peg-0.1.18.tar.gz | tar xz \
+    && make -C /peg-0.1.18 leg >/dev/null 2>&1 \
+    && mv /peg-0.1.18/leg /usr/bin/ \
+    && rm -r peg-0.1.18
+# Add project files and compile
+WORKDIR /javascrypt
+COPY . .
+RUN make

README.md

@@ -18,11 +18,23 @@ $ brew install bdw-gc
 $ make
 ```
 
+## Docker
+
+The Docker image provides a ready to go environment to experiment with the project. Just build the image locally and run an interactive shell inside the container:
+```bash
+$ docker build . --tag mtardy/javascrypt
+$ docker run -it mtardy/javascrypt
+```
+
 ## Usage
 
 ```bash
 $ echo "a=2+3 a*2" | ./calc
 ```
+or
+```bash
+$ ./calc < file
+```
 
 ## Tests