Fix md formatting for code blocks (can't check on localhost)

Author: nlharris

README.md

@@ -72,31 +72,37 @@ This may change.
 - To set up a URL redirect, add an alias to the page you want to
   redirect *to*. This goes in the header part of the .md (the part
   between the three dashes) and looks like this:
-[code]
+```
  aliases:
   - /events/bosc/
-  [/code]
+```
+
   - To include an image, you can use this markdown format:
-  [code]
+  ```
   ![alt text](image-path)
-  [/code]
+```
+
 - Images take up the full width of the page. If you want to scale an
 image, use this html:
-[code]
+```
 <img src="image-path" style="width:75%" alt="alt text" />
-[/code]
+```
+
 - When testing changes on localhost:1313, note that changes that
   involve .pngs take effect right away, but for some reason, if you're
   using .jpg or .jpeg images, it takes a while (20 min or so?) for
   them to show up on localhost. No idea why.
   - To enclose a section of text in a gray box use
-  [code]<div class="well">[/code]
+  ```
+  <div class="well">
+  ```
+  
 - To make two columns (e.g. to run text next to an image), use
 "columns" (look for an example in one of our .mds)
 - You can make a button like this:
-[code]
+```
 <a href="URL" class="btn btn-lg btn-primary">text on button</a>
-[/code]
+```
 
 ## Steps taken to port content from old WP site