Update README.md to improve 3 sections

Changes:
- The `Why?` link is updated from `why` to `why-gitlab`.
- The `Is it any good?` link was already redirecting to `why-gitlab`,
so that section is moved to `Why?`.
- The `Is it awesome?` link is 9 years old:
(c3007888). It may be the time to
make this change.

README.md

@@ -113,14 +113,10 @@ All documentation can be found on <https://docs.gitlab.com>.
 Please see [Getting help for GitLab](https://about.gitlab.com/getting-help/) on our website for the many options to get help.
-## Why?
-[Read here](https://about.gitlab.com/why/)
-
-## Is it any good?
-
-[Yes](https://about.gitlab.com/is-it-any-good/)
+## Why? Is it any good?
+Read [why our customers choose GitLab](https://about.gitlab.com/why-gitlab/).
 ## Is it awesome?
-[These people](https://twitter.com/gitlab/followers) seem to like it.
+[These people](https://about.gitlab.com/customers/) seem to like it.