Update sphinx config (#621)

* Update rtd_requirements for sphinx.

* Add readthedocs config v2,
diff --git a/.readthedocs.yml b/.readthedocs.yml
new file mode 100644
index 0000000..c52a552
--- /dev/null
+++ b/.readthedocs.yml
@@ -0,0 +1,25 @@
+# .readthedocs.yml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+  builder: html
+  configuration: docs/conf.py
+
+# Build documentation with MkDocs
+#mkdocs:
+#  configuration: mkdocs.yml
+
+# Optionally build your docs in additional formats such as PDF and ePub
+formats: all
+
+# Optionally set the version of Python and requirements required to build your docs
+python:
+  version: 3.7
+  install:
+    - requirements: docs/requirements.txt
+
diff --git a/docs/requirements.txt b/docs/requirements.txt
new file mode 100644
index 0000000..d9f0263
--- /dev/null
+++ b/docs/requirements.txt
@@ -0,0 +1,3 @@
+recommonmark
+sphinx
+mobly
\ No newline at end of file
diff --git a/docs/rtd_requirements.txt b/docs/rtd_requirements.txt
deleted file mode 100644
index d68bbad..0000000
--- a/docs/rtd_requirements.txt
+++ /dev/null
@@ -1,6 +0,0 @@
-alabaster==0.7.9
-CommonMark==0.5.4
-recommonmark==0.4.0
-Sphinx==1.5.2
-sphinx-autobuild==0.6.0
-mobly