Merge pull request #25569 from friism/fix-typo-in-security-doc

update intro to say there are four things to consider
(cherry picked from commit ce2ca236db87f8f580cb29be27b4f0b5341af0ca)

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>
(cherry picked from commit 7cee444f8b90d435cc3358e2f510d0614e4e02fd)
Signed-off-by: Tibor Vass <tibor@docker.com>

docs/security/security.md

@@ -12,7 +12,7 @@ weight =-99
 
 # Docker security
 
-There are three major areas to consider when reviewing Docker security:
+There are four major areas to consider when reviewing Docker security:
 
  - the intrinsic security of the kernel and its support for
    namespaces and cgroups;