add build instructions

BUILD.md

@@ -0,0 +1,24 @@
+# Building from Source
+
+To build the package from source, follow these steps:
+
+```
+$ pip install -r requirements.txt
+$ python setup.py sdist bdist_wheel
+```
+
+To test the package before uploading to PyPi:
+
+```
+$ python -m venv myenv
+$ source myenv/bin/activate
+$ pip install .
+$ pystructurizr dev --view example.containerview
+$ deactivate
+$ rm -fr myenv
+```
+
+# Deploying to PyPi
+```
+$ twine upload dist/*
+```