Merge pull request #10 from noffle/improvements

usage message + bugfix when using tslide in a pipe

index.js

@@ -12,6 +12,11 @@ var js = require('hipster/highlight/javascript')
 var imgcat = require('ansi-escapes').image
 
 var file = opts._[0]
+if (!file) {
+  console.error('USAGE: tslide [markdown-file]')
+  process.exit(1)
+}
+
 var text = require('fs').readFileSync(file, 'utf-8')
 var slides = text.split(/---+\n/)
 if(slides.length <= 1) {
@@ -64,7 +69,10 @@ function show () {
     .reset()
     .position(1, mtop)
     .write(indent(content, mleft))
-    .position(mleft, process.stdout.rows - 1)
+
+  if (process.stdout.rows) {
+    charm.position(mleft, process.stdout.rows - 1)
+  }
 }
 var index = 0
 show(index)