add in documenation for targeting an individual file

Also bump the docusaurus version

docs/installation.md

@@ -151,6 +151,13 @@ contained, by default the `docs/` directory is used.
 +  --in mydocs
 ```
 
+You can also target an individual file by passing it to `--in`.
+
+```diff
+ coursier launch org.scalameta:mdoc_@SCALA_BINARY_VERSION@:@VERSION@ -- \
++  --in mydocs/readme.md
+```
+
 Use `--site.VARIABLE=value` to add site variables that can be referenced from
 markdown as `@@VARIABLE@`.
 

mdoc-sbt/src/main/scala/mdoc/MdocPlugin.scala

@@ -18,8 +18,8 @@ object MdocPlugin extends AutoPlugin {
       )
     val mdocIn =
       settingKey[File](
-        "Input directory containing markdown sources to be processed by mdoc. " +
-          "Defaults to the toplevel docs/ directory."
+        "Input directory containing markdown sources to be processed by mdoc, or an " +
+          "individual file that you'd like to target. Defaults to the toplevel docs/ directory."
       )
     val mdocOut =
       settingKey[File](

mdoc/src/main/scala/mdoc/internal/cli/Settings.scala

@@ -35,9 +35,9 @@ class Section(val name: String) extends StaticAnnotation
 case class Settings(
     @Section("Common options")
     @Description(
-      "The input directory containing markdown and other documentation sources. " +
-        "Markdown files will be processed by mdoc while other files will be copied " +
-        "verbatim to the output directory."
+      "The input directory containing markdown and other documentation sources " +
+        "or an individual file that you'd like to target. Markdown files will be " +
+        "processed by mdoc while other files will be copied verbatim to the output directory."
     )
     @ExtraName("i")
     in: AbsolutePath,

website/package.json

@@ -9,6 +9,6 @@
     "rename-version": "docusaurus-rename-version"
   },
   "devDependencies": {
-    "docusaurus": "1.6.2"
+    "docusaurus": "1.14.4"
   }
 }