Mention Native Client buffer requirements.

Allow more convenient target hint setting.

doc/best-practices.dox

@@ -29,5 +29,14 @@ information.
 
 - [Best practices for 3D graphics](https://developers.google.com/native-client/beta/devguide/coding/3D-graphics#best-practices)
 
+@subsubsection best-practices-nacl-buffer-types Native Client requires unique buffer binding
+
+As noted in the above link, buffers in NaCl implementation need to be bound
+only to one unique target, i.e., Buffer bound to @ref Buffer::Target "Target::Array"
+cannot be later rebound to @ref Buffer::Target "Target::Element". However,
+%Magnum by default uses any sufficient target when binding the buffer
+internally (e.g. for setting data or copying). To avoid this, set target hint
+to desired target, either in constructor or using Buffer::setTargetHint().
+
 */
 }

src/Buffer.h

@@ -305,11 +305,13 @@ class MAGNUM_EXPORT Buffer {
 
         /**
          * @brief Constructor
+         * @param targetHint    Target hint, see setTargetHint() for more
+         *      information
          *
          * Generates new OpenGL buffer.
          * @see @fn_gl{GenBuffers}
          */
-        inline Buffer(): _targetHint(Target::Array) {
+        inline Buffer(Target targetHint = Target::Array): _targetHint(targetHint) {
             glGenBuffers(1, &_id);
         }