Simplify management of documentation dependencies

.builds/tests-pypi.yml

@@ -20,7 +20,7 @@ tasks:
   - setup: |
       sudo systemctl start docker
       cd vdirsyncer
-      make -e install-dev -e install-docs
+      make -e install-dev
   - test: |
       cd vdirsyncer
       # Non-system python is used for packages:

Makefile

@@ -40,9 +40,6 @@ ci-test-storage:
 	done
 	bash $(CODECOV_PATH) -c
 
-install-docs:
-	pip install -Ur docs-requirements.txt
-
 release-deb:
 	sh scripts/release-deb.sh debian jessie
 	sh scripts/release-deb.sh debian stretch
@@ -53,8 +50,7 @@ release-deb:
 install-dev:
 	pip install -U pip setuptools wheel
 	pip install -e .
-	pip install -Ur test-requirements.txt
-	pip install pre-commit
+	pip install -Ur test-requirements.txt -r docs-requirements.txt pre-commit
 	set -xe && if [ "$(REQUIREMENTS)" = "minimal" ]; then \
 		pip install -U --force-reinstall $$(python setup.py --quiet minimal_requirements); \
 	fi

docs-requirements.txt

@@ -1,3 +1,4 @@
+# This file is used by readthedocs.org
 sphinx != 1.4.7
 sphinx_rtd_theme
 setuptools_scm

docs/packaging.rst

@@ -76,7 +76,7 @@ take care of the HTML docs' formatting.
 You can find a list of dependencies in ``docs-requirements.txt``. Again, you
 can install those using pip with::
 
-    make install-docs
+    pip install -r docs-requirements.txt
 
 Then change into the ``docs/`` directory and build whatever format you want
 using the ``Makefile`` in there (run ``make`` for the formats you can build).