Add bash syntax highlighting to README.md.

README.md

@@ -8,14 +8,18 @@ Prometheus documentation site.
 You need to have a working Ruby environment set up and then install the
 necessary gems:
 
-    cd docs
-    bundle
+```bash
+cd docs
+bundle
+```
 
 ## Building
 
 To generate the static site, run:
 
-    bundle exec nanoc
+```bash
+bundle exec nanoc
+```
 
 The resulting static site will be stored in the `output` directory.
 
@@ -23,10 +27,12 @@ The resulting static site will be stored in the `output` directory.
 
 To run a local server that displays the generated site, run:
 
-    # Rebuild the site whenever relevant files change:
-    bundle exec guard
-    # Start the local development server:
-    bundle exec nanoc view
+```bash
+# Rebuild the site whenever relevant files change:
+bundle exec guard
+# Start the local development server:
+bundle exec nanoc view
+```
 
 You should now be able to view the generated site at
 [http://localhost:3000/](http://localhost:3000).