Document basic style for procedures

wiki/src/contribute/how/documentation/style_guide.mdwn

@@ -48,6 +48,30 @@
   And not *graphics adapters*, *graphics*, *graphical hardware*, or
   *video card*.
 
+- **procedures** (a series of steps)
+
+  - Keep the number of steps low within a procedure (for example, below
+    10, ideally 7). For longer procedures, split them and give each
+    section a title.
+
+  - Add a blank line between each step.
+
+  - Rely on the automatic numbered of Markdown and number all the steps
+    with `1.`
+
+  See also the *Microsoft Manual of Style: Procedures and technical
+  content*.
+
+  *For example*:
+
+<pre>
+1. Make sure that you are connected to the Internet.
+
+1. Start <span class="application">Software Sources</span>.
+
+1. Click on the <span class="guilabel">PPAs</span> button and then choose to <span class="button">Add a new PPA&hellip;</span>.
+</pre>
+
 - **network interface**, **Wi-Fi interface**
 
   And not *card*, *device*, or *adapter*.