chore: Added a Dockerfile to be able to easily build and test.

Dockerbuild/Dockerfile

@@ -0,0 +1,24 @@
+FROM ubuntu:20.04 as build
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+        libssl1.1 \
+        ca-certificates \
+        wget \
+        dirmngr \
+        gnupg \
+        apt-transport-https \
+        software-properties-common \
+        make \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
+RUN apt-add-repository 'deb https://download.mono-project.com/repo/ubuntu stable-focal main'
+RUN apt -y install mono-complete
+
+RUN wget https://packages.microsoft.com/config/ubuntu/20.04/packages-microsoft-prod.deb && \
+	dpkg -i packages-microsoft-prod.deb 
+
+RUN apt-get update; apt-get update && apt-get install -y dotnet-sdk-3.1 && apt-get install -y dotnet-sdk-6.0
+
+WORKDIR /twilio

Dockerbuild/README.md

@@ -0,0 +1,38 @@
+# Building Twilio project through Docker
+
+## Build your image
+
+In the root of the repository:
+
+Powershell/cmd:
+```pwsh
+docker build -t twiliobuild .\Dockerbuild\
+```
+bash:
+```bash
+docker build -t twiliobuild ./Dockerbuild/
+```
+
+## Restore/Compile/Test
+
+In the repository root:
+
+### Start the container:
+
+powershell:
+```pwsh
+docker run -it --rm -v ${PWD}:/twilio twiliobuild
+```
+bash:
+```bash
+docker run -it --rm -v $(pwd):/twilio twiliobuild
+```
+
+### Test
+In the shell:
+
+1) `dotnet restore`
+2) `dotnet build -c Release --no-restore`
+3) `dotnet test -c Release --no-build`
+
+Or just in one command `make test` 

README.md

@@ -137,6 +137,11 @@ To use a custom HTTP client with this helper library, please see the [Twilio doc
 
 The `Dockerfile` present in this repository and its respective `twilio/twilio-csharp` Docker image are currently used by Twilio for testing purposes only.
 
+## Docker build Image
+
+There is a [Dockerfile](Dockerbuild/) available for build/testing your code.
+
+
 ## Getting help
 
 If you need help installing or using the library, please check the [Twilio Support Help Center](https://support.twilio.com) first, and [file a support ticket](https://twilio.com/help/contact) if you don't find an answer to your question.