Add Functional Tests Status Badge to README file

[ceciliaavila]

Proposed Changes

Add a Badge in the Readme file with the status of the build and execution of the Functional Tests as part of the Nightly Build Pipeline.

Note: We left a link pointing to our test pipeline that needs to be replaced following these instructions:

1- Copy the Markdown as shown in the pictures below:

2- Replace the test markdown we left in the Readme file on this PR.

[coveralls]

Pull Request Test Coverage Report for Build 53996

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 76.16%

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Totals
Change from base Build 53863:	0.0%
Covered Lines:	4399
Relevant Lines:	5776

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💛 - Coveralls

[cleemullins]

No issues found in Microsoft.Bot.Builder.dll
No issues found in Microsoft.Bot.Builder.AI.Luis.dll
No issues found in Microsoft.Bot.Builder.AI.QnA.dll
No issues found in Microsoft.Bot.Builder.ApplicationInsights.dll
No issues found in Microsoft.Bot.Builder.Azure.dll
No issues found in Microsoft.Bot.Builder.Dialogs.dll
No issues found in Microsoft.Bot.Builder.TemplateManager.dll
No issues found in Microsoft.Bot.Configuration.dll
No issues found in Microsoft.Bot.Connector.dll
No issues found in Microsoft.Bot.Schema.dll

[cleemullins]

@ceciliaavila I didn't notice you had created a PR for this. I went ahead and did this same thing earlier today when I setup the Functional Build.