Fix spelling mistakes and english in new pitfalls docs

Author: dkubb

docs/pitfalls.md

@@ -1,6 +1,6 @@
 ---
 layout: default
-title: Commom Pitfalls
+title: Common Pitfalls
 body_id: docs
 created_at: Sun Apr 01 21:13:13 -0700 2012
 ---
@@ -14,32 +14,29 @@ encounter, along with work-arounds or solutions if possible.
 Implicit String property length
 -------------------------------
 
-When declaring a String property, DataMapper will add an implicit length of 50
-characters if nothing is explicitly declared.
+When declaring a String property, DataMapper will add an implicit limit of 50
+characters if no limit is explicitly declared.
 
 For example, the two class declarations have identical behaviour:
-
 {% highlight ruby linenos %}
 # with an implicit length
 class Post
   include DataMapper::Resource
 
   property :title, String
 end
-{% endhighlight %}
 
-{% highlight ruby linenos %}
 # with an explicit length
 class Post
   include DataMapper::Resource
 
   property :title, String, :length => 50
 end
 {% endhighlight %}
-
 The reason for this default is that DataMapper needs to know the underlying
 column constraints in order to add validations from the property definitions.
 Databases will often choose their own arbitrary length constraints if one is not
-declared (often 255 chars). We choose something a bit more restricted as a
-default because we wanted to encourage peolpe to declare it explicitly in their
-model, rather than relying on DM or the DB choosing an implicit limit.
+declared (often defaulting to 255 chars). We choose something a bit more
+restrictive as a default because we wanted to encourage peolpe to declare
+it explicitly in their model, rather than relying on DM or the DB choosing
+an arbitrary limit.