clarify npm install command in less docs

docs/less.html

@@ -717,8 +717,8 @@
   <div class="row">
     <div class="span4">
       <h3>Node with makefile</h3>
-      <p>Install the LESS command line compiler with npm by running the following command:</p>
-      <pre>$ npm install less</pre>
+      <p>Install the LESS command line compiler globally with npm by running the following command:</p>
+      <pre>$ npm install -g less</pre>
       <p>Once installed just run <code>make</code> from the root of your bootstrap directory and you're all set.</p>
       <p>Additionally, if you have <a href="https://github.com/mynyml/watchr">watchr</a> installed, you may run <code>make watch</code> to have bootstrap automatically rebuilt every time you edit a file in the bootstrap lib (this isn't required, just a convenience method).</p>
     </div><!-- /span4 -->

docs/templates/pages/less.mustache

@@ -641,8 +641,8 @@
   <div class="row">
     <div class="span4">
       <h3>{{_i}}Node with makefile{{/i}}</h3>
-      <p>{{_i}}Install the LESS command line compiler with npm by running the following command:{{/i}}</p>
-      <pre>$ npm install less</pre>
+      <p>{{_i}}Install the LESS command line compiler globally with npm by running the following command:{{/i}}</p>
+      <pre>$ npm install -g less</pre>
       <p>{{_i}}Once installed just run <code>make</code> from the root of your bootstrap directory and you're all set.{{/i}}</p>
       <p>{{_i}}Additionally, if you have <a href="https://github.com/mynyml/watchr">watchr</a> installed, you may run <code>make watch</code> to have bootstrap automatically rebuilt every time you edit a file in the bootstrap lib (this isn't required, just a convenience method).{{/i}}</p>
     </div><!-- /span4 -->