feat(docs): build docs using docker image

Fixed requirements and redo a howto

docs/.howto

@@ -0,0 +1,6 b''
+## BUILD
+# cd docs
+# docker build --tag sphinx-doc-build .
+
+# Build Docs
+# docker run --rm -v $PWD:/project --workdir=/project/docs sphinx-doc-build make clean html
  No newline at end of file

docs/Dockerfile

@@ -1,10 +1,5 b''
-## BUILD
-# docker build --tag sphinx-doc-build .
-
-# Build Docs
-# docker run --rm -v $PWD:/docs --workdir=/project/docs sphinx-doc-build  make clean html
 FROM sphinxdoc/sphinx
 
 WORKDIR /project
-ADD requirement_docs.txt /project
-RUN pip3 install -r requirement_docs.txt
+ADD requirements_docs.txt /project
+RUN pip3 install -r requirements_docs.txt