Improved wording for the "light" heading sentences for the main dashboard pages

These are just a few very particular fixes for small grammatical issues,
intended to polish the reading experience.

app/views/dashboard/issues.html.haml

@@ -3,7 +3,7 @@
   %span.pull-right #{@issues.total_count} issues
 %p.light
-  For all issues you should visit project issues page. Or you can use search panel to find specific issue
+  For all issues you should visit the project's issues page. Or use the search panel to find a specific issue.
 %hr
 .row

app/views/dashboard/merge_requests.html.haml

@@ -4,7 +4,7 @@
 %p.light
-  Only merge requests authored or assigned to you are listed here.
+  Only merge requests created by you or assigned to you are listed here.
 %hr
 .row
   .span3

app/views/dashboard/projects.html.haml

 %h3.page-title My Projects
 %p.light
-  All projects you have access to are listed here. Public projects are not included here unless you have membership in it
+  All projects you have access to are listed here. Public projects are not included here unless you have membership in them
 %hr
 .row
   .span3