Updated CONTRIBUTING.md (#1233)

Author: tamojit-123

CONTRIBUTING.md

@@ -64,7 +64,7 @@ Before you submit your pull request consider the following guidelines:
 * Make your changes in a new git branch:
 
      ```shell
-     git checkout -b my-fix-branch master
+     $ git checkout -b my-fix-branch master
      ```
 
 * Create your patch, **including appropriate test cases**.
@@ -73,20 +73,20 @@ Before you submit your pull request consider the following guidelines:
 * Commit your changes using a descriptive commit message.
 
      ```shell
-     git commit -a
+     $ git commit -a
      ```
   Note: the optional commit `-a` command line option will automatically "add" and "rm" edited files.
 
 * Build your changes locally to ensure all the tests pass:
 
     ```shell
-   ./gradlew build
+   $ ./gradlew build
     ```
 
 * Push your branch to GitHub:
 
     ```shell
-    git push origin my-fix-branch
+    $ git push origin my-fix-branch
     ```
 
 * In GitHub, send a pull request to `firebase-quickstart-android:master`.
@@ -95,8 +95,8 @@ Before you submit your pull request consider the following guidelines:
   * Rebase your branch and force push to your GitHub repository (this will update your Pull Request):
 
     ```shell
-    git rebase master -i
-    git push origin my-fix-branch -f
+    $ git rebase master -i
+    $ git push origin my-fix-branch -f
     ```
 
 That's it! Thank you for your contribution!
@@ -109,25 +109,25 @@ from the main (upstream) repository:
 * Delete the remote branch on GitHub either through the GitHub Android UI or your local shell as follows:
 
     ```shell
-    git push origin --delete my-fix-branch
+    $ git push origin --delete my-fix-branch
     ```
 
 * Check out the master branch:
 
     ```shell
-    git checkout master -f
+    $ git checkout master -f
     ```
 
 * Delete the local branch:
 
     ```shell
-    git branch -D my-fix-branch
+    $ git branch -D my-fix-branch
     ```
 
 * Update your master with the latest upstream version:
 
     ```shell
-    git pull --ff upstream master
+    $ git pull --ff upstream master
     ```
 
 ## <a name="rules"></a> Coding Rules