Update Dockerfile

Author: Bill W

pdf2txt/alpine/Dockerfile

@@ -5,7 +5,7 @@
 # $ alias pdf2txt="docker run -ti --rm -v ~/app:/app pdf2txt"
 # $pdf2txt sample.pdf > sample.txt
 
-# You will get the txt file named `sample.txt` in ~/app folder.
+# You will get the txt file named `sample.txt` in current folder.
 
 # You can directly run below command to convert the pdf file in current foler.
 # $ docker run -ti --rm -v $(pwd):/app pdf2txt sample.pdf > sample.txt