Docs on alternative steps to clone the repo (#12107)

CONTRIBUTING.md

@@ -8,6 +8,7 @@ This guide is not definitive and it's being updated over time. If you find any i
 
 1. [Prerequisites](#prerequisites)
    1. [Tools](#tools)
+   2. [Cloning the repository](#cloning-the-repository)
 2. [Getting help](#getting-help)
 3. [Writing an extension](#writing-an-extension)
    1. [Setting up a new Gradle module](#setting-up-a-new-gradle-module)
@@ -49,6 +50,69 @@ Before you start, please note that the ability to use following technologies is
 - Emulator or phone with developer options enabled and a recent version of Tachiyomi installed
 - [Icon Generator](https://as280093.github.io/AndroidAssetStudio/icons-launcher.html)
 
+### Cloning the repository
+
+Some alternative steps can be followed to ignore "repo" branch and skip unrelated sources, which will make it faster to pull, navigate and build. This will also reduce disk usage and network traffic.
+
+<details><summary>Steps</summary>
+
+1. Make sure to delete "repo" branch in your fork.
+2. Do a partial clone.
+    ```bash
+    git clone --filter=blob:none --no-checkout <fork-repo-url>
+    cd tachiyomi-extensions/
+    ```
+3. Configure sparse checkout.
+    ```bash
+    # enable sparse checkout
+    git sparse-checkout set
+    # edit sparse checkout filter
+    vim .git/info/sparse-checkout
+    # alternatively, if you have VS Code installed
+    code .git/info/sparse-checkout
+    ```
+    Here's an example:
+    ```bash
+    /*
+    !/src/*
+    !/multisrc/overrides/*
+    !/multisrc/src/main/java/eu/kanade/tachiyomi/multisrc/*
+    # allow a single source
+    /src/<lang>/<source>
+    # allow a multisrc theme
+    /multisrc/src/main/java/eu/kanade/tachiyomi/multisrc/<source>
+    /multisrc/overrides/<source>
+    ```
+4. Configure remotes.
+    ```bash
+    # add upstream
+    git remote add upstream <tachiyomiorg-repo-url>
+    # optionally disable push to upstream
+    git remote set-url --push upstream no_pushing
+    # ignore 'repo' branch of upstream
+    # option 1: use negative refspec
+    git config --add remote.upstream.fetch "^refs/heads/repo"
+    # option 2: fetch master only (ignore all other branches)
+    git config remote.upstream.fetch "+refs/heads/master:refs/remotes/upstream/master"
+    # update remotes
+    git remote update
+    # track master of upstream instead of fork
+    git branch master -u upstream/master
+    # checkout
+    git switch master
+    ```
+5. Useful configurations. (optional)
+    ```bash
+    # prune obsolete remote branches on fetch
+    git config remote.origin.prune true
+    # fast-forward only when pulling master branch
+    git config pull.ff only
+    ```
+6. Later, if you change the sparse checkout filter, run `git sparse-checkout reapply`.
+
+Read more on [partial clone](https://github.blog/2020-12-21-get-up-to-speed-with-partial-clone-and-shallow-clone/), [sparse checkout](https://github.blog/2020-01-17-bring-your-monorepo-down-to-size-with-sparse-checkout/) and [negative refspecs](https://github.blog/2020-10-19-git-2-29-released/#user-content-negative-refspecs).
+</details>
+
 ## Getting help
 
 - Join [the Discord server](https://discord.gg/tachiyomi) for online help and to ask questions while developing your extension. When doing so, please ask it in the `#programming` channel.