doc: update coding guideline to suggest to place local imports last

It seems very common in other Go based projects to place the local
packages in the import statement last. Currently Ceph-CSI expects the
imports to group the local packages immediately after standard packages.
This exception compared to other projects often requires new
contributors to 'correct' their PR.

Following a more common convention for grouping imports should make it a
little easier to contribute to the project.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

docs/coding.md

@@ -18,14 +18,14 @@ the code and will be pointed out in the review process:
 
 ### Imports
 
-We use the following convention for specifying imports:
+We prefer the following convention for specifying imports:
 
 ```
 <import standard library packages>
 
-<import ceph-csi packages>
-
 <import third-party packages>
+
+<import ceph-csi packages>
 ```
 
 Example:
@@ -37,9 +37,9 @@ import (
  "strings"
  "time"
 
- "github.com/ceph/ceph-csi/internal/util"
-
  "github.com/pborman/uuid"
+
+ "github.com/ceph/ceph-csi/internal/util"
 )
 ```