Updated Symmteric and Asymmetric Encryption Description

[dmagnate]

Thank you for submitting a Pull Request to the Mobile Security Testing Guide. Please make sure that:

• Your contribution is written in the 2nd person (e.g. you)
• Your contribution is written in an active present form for as much as possible.
• You have made sure that the reference section is up to date (e.g. please add sources you have used, make sure that the references to MITRE/MASVS/etc. are up to date)
• Your contribution has proper formatted markdown and/or code
• Any references to website have been formatted as [TEXT](URL “NAME”)
• You verified/tested the effectiveness of your contribution (e.g.: is the code really an effective remediation? Please verify it works!)

If your PR is related to an issue. Please end your PR test with the following line:
This PR closes #< insert number here >.

[TheDauntless]

Thanks for contributing! 🥳

I've made a few additional modifications; can you please accept the proposed changes so that we can merge your contributions? :)

[dmagnate]

Thanks for the review and update @TheDauntless

[TheDauntless]

🥳

[cpholguera]

Thank you @dmagnate!