fix: Documentation for mermaid configuration and note about theme set…

…ting via env variable

README.md

@@ -81,6 +81,8 @@ Options
 -   dark
 -   neutral
 
+This option does not accept environment variables or other dynamic values. If you want to change the theme dynamically, you can use the `theme` option in the `mermaidConfig` option. See [Mermaid Configuration](#mermaid-configuration) for more information.
+
 ### mmdcPath
 
 In order for this generator to succeed you must have `mmdc` installed. This is the mermaid cli tool that is used to generate the ERD. By default the generator searches for an existing binary file at `/node_modules/.bin`. If it fails to find that binary it will run `find ../.. -name mmdc` to search through your folder for a `mmdc` binary. If you are using a different package manager or have a different location for your binary files, you can specify the path to the binary file.
@@ -202,6 +204,17 @@ generator erd {
 }
 ```
 
+### Mermaid configuration
+
+Overriding the default mermaid configuration may be necessary to represent your schema in the best way possible. There is an example mermaid config [here](./example-mermaid-config.js) that you can use as a starting point. In the example JavaScript file, types are referenced to view all available options. You can also view them [here](https://github.com/mermaid-js/mermaid/blob/master/packages/mermaid/src/defaultConfig.ts). The most common use cases for needing to overwrite mermaid configuration is for theming and default sizing of the ERD.
+
+```prisma
+generator erd {
+  provider = "prisma-erd-generator"
+  mermaidConfig = "mermaidConfig.json"
+}
+```
+
 ### Puppeteer configuration
 
 If you want to change the configuration of Puppeteer, create a [Puppeteer config file (JSON)](https://pptr.dev/guides/configuration#configuration-files) and pass the file path to the generator.