Add troubleshooting note to demo

.gitlab-ci.yml

@@ -32,4 +32,4 @@ build:
   stage: build
   script:
     - apt-get update && apt-get install -y libasound2-dev
-    - go build -race
+    - go build

README.md

@@ -15,6 +15,11 @@ If you are running Linux with ALSA, you can try ditty without installing:
 
 ```ssh ditty.rocketnine.space -p 20020 2> >(aplay --quiet)```
 
+If you can't hear anything, you may need to specify which device ```aplay```
+should use with ```-D```.
+
+To list available sound devices, execute ```aplay -l```.
+
 ## Install
 
 Choose one of the following methods:
@@ -36,7 +41,7 @@ go get gitlab.com/tslocum/ditty
 * [mewkiz/flac](https://github.com/mewkiz/flac)
 * [hajimehoshi/go-mp3](https://github.com/hajimehoshi/go-mp3)
 * [jfreymuth/oggvorbis](https://github.com/jfreymuth/oggvorbis)
-* [tslocum/cview](https://github.com/tslocum/cview)
+* [tslocum/cview](https://gitlab.com/tslocum/cview)
 
 ## Documentation