[enh] Add security info

README.md

@@ -1,2 +1,5 @@
 # issues
 General issue tracker for the YunoHost project
+
+**/!\ If you have found a security issue, please follow https://yunohost.org/en/security_team **
+

SECURITY.md

@@ -0,0 +1,2 @@
+# Security Policy
+See https://yunohost.org/en/security_team

issue_template.md

@@ -4,6 +4,8 @@ about: When creating a bug report, please use the following template to determin
 
 ---
 
+**/!\ If you have found a security issue, please follow https://yunohost.org/en/security_team **
+
 **How to post a meaningful bug report**
 1. *Read this whole template first.*
 2. *Determine if you are on the right place:*