Add common security risks lesson (#21)

* init security risks session

* spelling, backgroung color at end

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Co-authored-by: Nuke <[email protected]>

Author: patriciobcs

content/SUMMARY.md

@@ -144,6 +144,7 @@
   - [User Centric](./security/user-centric/page.md)
   - [Infrastructure](./security/infrastucutre/page.md)
   - [Application](./security/appsec/page.md)
+  - [Common Security Risks](./security/risks/page.md)
 
 - [𝞨 Formal Methods for Rust](./formal-methods/intro/page.md)