Add BuiltWithDot.Net badge to README

[Corstiaan84]

Since Exceptionless is listed on BuiltWithDot.Net I've taken the liberty to raise a PR that adds the BuiltWithDot.Net badge for Exceptionless to the README.md file. This will help promote your project, BuiltWithDot.Net, all other .NET developers that have projects listed on the site, and the open-source .NET ecosystem in general. If you have any questions or concerns, please let me know. Your help is much appreciated!

Thanks, Corstiaan (creator of BuiltWithDot.Net)

PS If you don't want to add the badge, that's totally fine. Just close this PR. No hard feelings :-)

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ niemyjski
❌ Corstiaan84
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[niemyjski]

Thanks for the pr!