Small typo fixes in readme.md files

[jdewinkel]

Description

This pull request solves some minor typo's in two readme.md files.
events/README.md and features/mbedtls/README.md

Pull request type

• Fix
• Refactor
• New target
• Feature
• Breaking change

[cmonr]

Hi @jdewinkel. Thanks for the minor fixes.
Would you mind signing the CLA: https://developer.mbed.org/contributor_agreement/ ?

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1368
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6286/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[jdewinkel]

Hey, @cmonr I have already signed the CLA.

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1019
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6286/

[mbed-ci]

Test : SUCCESS

Build number : 1149
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6286/1149

[0xc0170]

/morph mbed2-build