Minor formatting updates for gvisor.dev.

* Aggregate architecture Overview in "What is gVisor?" as it makes more sense
  in one place.

* Drop "user-space kernel" and use "application kernel". The term "user-space
  kernel" is confusing when some platform implementation do not run in
  user-space (instead running in guest ring zero).

* Clear up the relationship between the Platform page in the user guide and the
  Platform page in the architecture guide, and ensure they are cross-linked.

* Restore the call-to-action quick start link in the main page, and drop the
  GitHub link (which also appears in the top-right).

* Improve image formatting by centering all doc and blog images, and move the
  image captions to the alt text.

PiperOrigin-RevId: 311845158

1 files changed, 1 insertions, 7 deletions

diff --git a/website/blog/2020-04-02-networking-security.md b/website/blog/2020-04-02-networking-security.md
index 78f0a6714..5a5e38fd7 100644
--- a/website/blog/2020-04-02-networking-security.md
+++ b/website/blog/2020-04-02-networking-security.md
@@ -69,13 +69,7 @@ a similar syscall). Moreover, because packets typically come from off-host (e.g.
 the internet), the Host OS's packet processing code has received a lot of
 scrutiny, hopefully resulting in a high degree of hardening.
 
---------------------------------------------------------------------------------
-
-![Figure 1](/assets/images/2020-04-02-networking-security-figure1.png)
-
-Figure 1: Netstack and gVisor
-
---------------------------------------------------------------------------------
+![Figure 1](/assets/images/2020-04-02-networking-security-figure1.png "Network and gVisor.")
 
 ## Writing a network stack