docs: add restriction on matchCurrentVersion (#21485)

Co-authored-by: Rhys Arkins <rhys@arkins.net>

docs/usage/configuration-options.md

@@ -2031,7 +2031,7 @@ The `currentVersion` field will be one of the following (in order of preference)
 
 Consider using instead `matchCurrentValue` if you wish to match against the raw string value of a dependency.
 
-`matchCurrentVersion` can be an exact SemVer version or a SemVer range:
+`matchCurrentVersion` can be an exact version or a version range:
 
 ```json
 {
@@ -2044,6 +2044,10 @@ Consider using instead `matchCurrentValue` if you wish to match against the raw
 }
 ```
 
+The syntax of the version range must follow the [versioning scheme](https://docs.renovatebot.com/modules/versioning/#supported-versioning) used by the matched package(s).
+This is usually defined by the [manager](https://docs.renovatebot.com/modules/manager/#supported-managers) which discovered them or by the default versioning for the package's [datasource](https://docs.renovatebot.com/modules/datasource/).
+For example, a Gradle package would typically need Gradle constraint syntax (e.g. `[,7.0)`) and not SemVer syntax (e.g. `<7.0`).
+
 This field also supports Regular Expressions which must begin and end with `/`.
 For example, the following enforces that only `1.*` versions will be used: