[REF] Major revamp after introducing --output /dev/stdout in upstream

Ref:
* mermaid-js/mermaid-cli#725
* https://hub.docker.com/r/minlag/mermaid-cli/tags

Dropping the whole image building, simply using the upstream pre-built image
with options to specify own images and tags. Didn't work on MacOS anyway
because `google-chrome-stable` was unavailable on `linux/arm64` platform when
building the image. The upstream image supports `linux/arm64` out-of-box, so it
*should* work on MacOS.

README.md

@@ -7,12 +7,11 @@
 
 Render mermaid graphs with Docker service
 
-This library attempts to create Mermaid graphs via
-[mermaid.ink](https://github.com/jihchi/mermaid.ink) aka
-[mermaid](https://mermaid.js.org/) as an API via a custom locally-built Docker
-image with restricted network access, so that you are sure nothing gets out and
-your system is kept isolated from random Node.js deps/files noise all around
-the filesystem.
+This library attempts to create Mermaid graphs via the official
+[`mermaid-cli`](https://github.com/mermaid-js/mermaid-cli) using the official
+Docker image and restricting network access, so that you are sure nothing gets
+out and your system is kept isolated from random Node.js deps/files noise all
+around the filesystem.
 
 ## How to