git-subtree: add page (#4012)

Co-authored-by: Zlatan Vasović <zlatanvasovic@gmail.com>
Co-authored-by: Andrik Albuquerque <andrik.albuquerque@gmail.com>
Co-authored-by: Starbeamrainbowlabs <sbrl@starbeamrainbowlabs.com>

pages/common/git-subtree.md

@@ -0,0 +1,24 @@
+# git subtree
+
+> Tool to manage project dependencies as subprojects.
+> More information: <https://manpages.debian.org/testing/git-man/git-subtree.1.en.html>.
+
+- Add a git repository as a subtree:
+
+`git subtree add --prefix={{path/to/directory/}} --squash {{repository_url}} {{master}}`
+
+- Update subtree repository to its latest commit:
+
+`git subtree pull --prefix={{path/to/directory/}} {{repository_url}} {{master}}`
+
+- Merge a subtree repository into master:
+
+`git subtree merge --prefix={{path/to/directory/}} --squash {{repository_url}} {{master}}`
+
+- Push commits to a subtree repository:
+
+`git subtree push --prefix={{path/to/directory/}} {{repository_url}} {{master}}`
+
+- Extract a new project history from the history of a subtree:
+
+`git subtree split --prefix={{path/to/directory/}} {{repository_url}} -b {{branch_name}}`