update README

README.md

@@ -17,9 +17,9 @@ Optional:
 
 Download the [backend package][deckjs] and use asciidoc to install:
 
-```bash
+~~~~.bash
 asciidoc --backend install deckjs-1.2.zip
-```
+~~~~
 
 This will install the backend to `~/asciidoc/backend/deckjs`.
 
@@ -30,17 +30,17 @@ You can also use this backend without installation, see the next section.
 
 * With deckjs backend installed, use following command to generate slides:
 
-```bash
+~~~~.bash
 asciidoc -b deckjs file.asciidoc
-```
+~~~~
 
 By default, the `linkcss` option is disabled so all the required js and css file will be embedded into the output slide. Checkout the [template file][example] for how to enable all kinds of options.
 
 * To use without Installation, you need to specify different argument:
 
-```bash
+~~~~.bash
 asciidoc -f deck.js.conf file.asciidoc
-```
+~~~~
 
 Make sure your asciidoc can properly find `deckjs.conf`. For asciidoc's configuration file loading strategy, please refer to [this guide][asc-conf-guide].