HTTPS links in Docs

I didn't touch old release notes and some code examples.
All links were tested and in some cases updated to prevent redirects where URLs have changed.

content/en/getting-started/usage.md

@@ -36,7 +36,7 @@ hugo is the main command, used to build your Hugo site.
 Hugo is a Fast and Flexible Static Site Generator
 built with love by spf13 and friends in Go.
 
-Complete documentation is available at http://gohugo.io/.
+Complete documentation is available at https://gohugo.io/.
 
 Usage:
   hugo [flags]
@@ -56,7 +56,7 @@ Available Commands:
   version     Print the version number of Hugo
 
 Flags:
-  -b, --baseURL string         hostname (and path) to the root, e.g. http://spf13.com/
+  -b, --baseURL string         hostname (and path) to the root, e.g. https://spf13.com/
   -D, --buildDrafts            include content marked as draft
   -E, --buildExpired           include expired content
   -F, --buildFuture            include content with publishdate in the future