Installation: document COURSIER_REPOSITORIES

docs/configuration.md

@@ -91,6 +91,9 @@ formatter, the correct release will be downloaded dynamically.
 
 > Since v3.1.0, the `version` parameter is required to be specified explicitly.
 
+Since that requires access to artifact repositories, please see more on that on the
+[Installation](installation.md#using-custom-repositories-with-cli) page.
+
 ## Scala Dialects
 
 The formatter supports various dialects defined and supported by `scalameta` parser. However,

docs/installation.md

@@ -378,6 +378,34 @@ println(website.plaintext(org.scalafmt.cli.CliArgParser.buildInfo))
 println(website.plaintext(org.scalafmt.cli.CliArgParser.scoptParser.usage))
 ```
 
+### Using custom repositories with CLI
+
+Under the hood, `scalafmt` uses the `scalafmt-dynamic` library and, in turn,
+`coursier`, to download the version (of `scalafmt-core`) specified in
+`.scalafmt.conf` file.
+
+By default, coursier will download from a few standard repositories (including
+sonatype, both public and snapshot). However, if you'd like to use instead some
+custom repositories within your environment, please specify them using the
+`COURSIER_REPOSITORIES` environment variable.
+
+#### Repository credentials
+
+Additionally, if your repositories require credentials, please specify them
+in the [`COURSIER_CREDENTIALS`](https://get-coursier.io/docs/other-credentials)
+environment variable.
+
+Keep in mind that `coursier` credential format is not the same as, say, `sbt`,
+and since multiple entries are allowed and expected, each requires a unique
+prefix of your choosing.
+
+Others have also reported needing to include in their credentials settings such as
+
+```
+<prefix>.pass-on-redirect=true
+<prefix>.auto=true
+```
+
 ## Gradle
 
 It is possible to use scalafmt in gradle with the following externally