Add README.md

README.md

+To create the binaries for a new version of either Alpine or wkhtmltopdf, use this `Dockerfile` and adjust the version tags:
+
+```
+FROM surnet/alpine-wkhtmltopdf:3.17.0-0.12.6-full as wkhtmltopdf
+FROM php:8.2-fpm-alpine3.17 AS app
+
+# wkhtmltopdf install dependencies
+RUN apk add --no-cache \
+        libstdc++ \
+        libx11 \
+        libxrender \
+        libxext \
+        libssl1.1 \
+        ca-certificates \
+        fontconfig \
+        freetype \
+        ttf-droid \
+        ttf-freefont \
+        ttf-liberation \
+        # more fonts
+        ;
+
+# wkhtmltopdf copy bins from ext image
+COPY --from=wkhtmltopdf /bin/wkhtmltopdf /bin/libwkhtmltox.so /bin/
+```
+
+Create an image with `docker build -t phpwithwkhtmltopdf .` and when completed, start the container with `docker run --rm --name wkhtml phpwithwkhtmltopdf` to then extract the binaries:
+
+```
+docker cp wkhtml:/bin/wkhtmltopdf .
+docker cp wkhtml:/bin/libwkhtmltox.so .
+```