Add citation-file-formatting repository as submodule (asreview#894)

.github/workflows/ci-core.yml

@@ -5,7 +5,7 @@ jobs:
     name: lint-python
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v2
     - uses: actions/setup-python@v1
       with:
         python-version: '3.8'
@@ -20,7 +20,9 @@ jobs:
     name: test-minimal-deps
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v2
+      with:
+        submodules: recursive
     - uses: actions/setup-python@v1
       with:
         python-version: '3.8'
@@ -36,7 +38,9 @@ jobs:
     name: test-full-deps
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v2
+      with:
+        submodules: recursive
     - uses: actions/setup-python@v1
       with:
         python-version: '3.8'

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "tests/citation-file-formatting"]
+	path = tests/citation-file-formatting
+	url = https://github.com/asreview/citation-file-formatting.git

DEVELOPMENT.md

@@ -9,6 +9,17 @@ Build the project from source with the following code.
 
 ## Development workflow
 
+### Git Submodules
+Some demo datasets are included as a submodule. Directory [asreview/tests/citation-file-formatting](https://github.com/ottomattas/asreview/tree/development-v1/tests) is cloned from [citation-file-formatting](https://github.com/asreview/citation-file-formatting).
+
+Examples:
+- To clone the full repository with submodules in one line, add `--recursive` flag:
+
+	```git clone --recursive git://github.com/asreview/asreview.git```
+
+- To update the submodule, you would still need to follow the contribution guide in the submodule repository. And then create a PR for the main repository with the updated submodule commit.
+
+
 ### Back end
 Install Python