PON requirement docs and seq diagrams

Please review and comment.

Change-Id: Iccec623e25bd723816c235cd4dd1a3b6d54e7d85
diff --git a/docs/Makefile b/docs/Makefile
new file mode 100644
index 0000000..8d9e615
--- /dev/null
+++ b/docs/Makefile
@@ -0,0 +1,50 @@
+#
+# Copyright 2016 the original author or authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+ifeq ($(VOLTHA_BASE)_set,_set)
+$(error To get started, please source the env.sh file)
+endif
+
+default: build
+
+GENERATED_SVG_FILES := \
+	pon-requirements/reference-inband.svg \
+	pon-requirements/reference-internal.svg \
+	pon-requirements/olt-states.svg
+
+build: checkdiag $(GENERATED_SVG_FILES)
+	@echo "Building drawings"
+
+%.svg: %.block
+	blockdiag -T svg -o $@ $<
+
+%.svg: %.seq
+	seqdiag -T svg -o $@ $<
+
+clean:
+	rm -f $(GENERATED_SVG_FILES)
+
+checkdiag:
+	@if ! blockdiag --version > /dev/null; then \
+	  echo "Installing blockdiag..."; \
+	  pip install blockdiag; \
+	fi
+	@if ! seqdiag --version > /dev/null; then \
+	  echo "Installing seqdiag..."; \
+	  pip install seqdiag; \
+	fi
+	@echo "Tools ready"
+