git-stage: add page (#3963)

* git-stage: add page

* Apply suggestions from code review

Co-Authored-By: Starbeamrainbowlabs <sbrl@starbeamrainbowlabs.com>

* Update git-add.md

* Update git-stage.md

Co-authored-by: Starbeamrainbowlabs <sbrl@starbeamrainbowlabs.com>

pages/common/git-add.md

@@ -26,3 +26,7 @@
 - Interactively stage parts of a given file:
 
 `git add -p {{path/to/file}}`
+
+- Interactively stage a file:
+
+`git add -i`

pages/common/git-stage.md

@@ -0,0 +1,33 @@
+# git stage
+
+> Add file contents to the staging area.
+> Synonym of `git add`.
+> More information: <https://git-scm.com/docs/git-stage>.
+
+- Add a file to the index:
+
+`git stage {{path/to/file}}`
+
+- Add all files (tracked and untracked):
+
+`git stage -A`
+
+- Only add already tracked files:
+
+`git stage -u`
+
+- Also add ignored files:
+
+`git stage -f`
+
+- Interactively stage parts of files:
+
+`git stage -p`
+
+- Interactively stage parts of a given file:
+
+`git stage -p {{path/to/file}}`
+
+- Interactively stage a file:
+
+`git stage -i`