Updated upcloud.rst
Updated upcloud.rst

- Revised the wording
- Added 'Enabling API access' section

Signed-off-by: Quentin Pradet <d17611fde61d73f8de1b8b01bc47d446558ccd8e@apache.org>

StackPointCloud/libcloud,pquentin/libcloud,Scalr/libcloud,vongazman/libcloud,ByteInternet/libcloud,pquentin/libcloud,vongazman/libcloud,StackPointCloud/libcloud,apache/libcloud,erjohnso/libcloud,andrewsomething/libcloud,andrewsomething/libcloud,Scalr/libcloud,Kami/libcloud,Scalr/libcloud,apache/libcloud,ByteInternet/libcloud,andrewsomething/libcloud,StackPointCloud/libcloud,ByteInternet/libcloud,pquentin/libcloud,mistio/libcloud,mistio/libcloud,apache/libcloud,mistio/libcloud,Kami/libcloud,Kami/libcloud,erjohnso/libcloud,erjohnso/libcloud,vongazman/libcloud