Improve Docker readme regarding index preparation

Change-Id: I1a5e79ce320b2fa1a615dfb25e7851ee129f79ae
diff --git a/Readme.md b/Readme.md
index 48fbbf4..62962e4 100644
--- a/Readme.md
+++ b/Readme.md
@@ -11,7 +11,8 @@
 In addition, all relevant tools are installed and
 made available that are necessary for data conversion
 and indexing of corpora in the widely used TEI-P5
-([I5](https://www.ids-mannheim.de/en/digspra/corpus-linguistics/projects/corpus-development/ids-text-model/)) format for KorAP.
+([I5](https://www.ids-mannheim.de/en/digspra/corpus-linguistics/projects/corpus-development/ids-text-model/))
+format for KorAP.
 For different options of the tools we refer to the
 respective repositories.
 
@@ -24,8 +25,14 @@
 
 ## Starting
 
-To download, intialize and run KorAP pointing to an existing index
-(in this example `index` in the local directory), run
+To get KorAP running, an existing index is required.
+For testing, either download the sample index provided by
+[Kustvakt](https://github.com/KorAP/Kustvakt/tree/master/sample-index)
+or first follow the instructions on [Corpus Conversion](#corpus-conversion).
+
+To download, intialize and run KorAP pointing to that existing index
+(in this example stored in the `index` folder in the local directory),
+run
 
 ```shell
 $ INDEX=./index docker-compose --profile=lite up