Better header and detail why you need two times the storage. Also moving...

Better header and detail why you need two times the storage. Also moving memory and storage to the bottom, OS is more important.

doc/install/requirements.md

-# Memory
-
-We recommend you to run GitLab on a server with at least 1GB of RAM memory. You can use it with 512MB of memory but you need to setup unicorn to use only 1 worker and you need at least 200MB of swap. On a server with 1.5GB of memory you are able to support 1000+ users.
-
-
-# Hard disk capacity
-
-The necessary hard disk space largely depends on the size of the repos you want
-to store in GitLab. But as a *rule of thumb* you should have at least twice as much
-free space as your all repos combined take up. Apart from a local hard drive you can also mount a volume that supports the network file system (NFS) protocol. This volume might be located on a file server, a network attached storage (NAS) device, a storage area network (SAN) or on an Amazon Web Services (AWS) Elastic Block Store (EBS) volume.
-
-
 # Operating Systems
 
 ## Linux
@@ -41,7 +29,6 @@ GitLab does **not** run on Windows and we have no plans of supporting it in the
 near future. Please consider using a virtual machine to run GitLab.
 
 
-
 # Rubies
 
 GitLab requires Ruby (MRI) 1.9.3 and several Gems with native components.
@@ -50,6 +37,17 @@ While it is generally possible to use other Rubies (like
 some work on your part.
 
 
+# Memory
+
+We recommend you to run GitLab on a server with at least 1GB of RAM memory. You can use it with 512MB of memory but you need to setup unicorn to use only 1 worker and you need at least 200MB of swap. On a server with 1.5GB of memory you are able to support 1000+ users.
+
+
+# Storage
+
+The necessary hard disk space largely depends on the size of the repos you want
+to store in GitLab. But as a *rule of thumb* you should have at least twice as much
+free space as your all repos combined take up. You need twice the storage because [GitLab satellites](https://github.com/gitlabhq/gitlabhq/blob/master/doc/install/structure.md) contain an extra copy of each repo. Apart from a local hard drive you can also mount a volume that supports the network file system (NFS) protocol. This volume might be located on a file server, a network attached storage (NAS) device, a storage area network (SAN) or on an Amazon Web Services (AWS) Elastic Block Store (EBS) volume.
+
 
 # Installation troubles and reporting success or failure