Corrected some grammar and typo's

line 17 : :guilabel:`Plugins > Manage and install pluginsi ...`.   ---> ' pluginsi' should be  'plugins'
 
line 21:  some plugins updating ------> 'some plugins updating' should be 'some updates for plugins'
Merge pull request #410 from DiGro/patch-1

Corrected some grammar and typo's