Added Merge Conflict section to Best Practices doc

docs/newbs_best_practices.md

@@ -9,6 +9,7 @@ This document assumes a few things:
 1. You have a GitHub account, and have [forked the qmk_firmware repository](getting_started_github.md) to your account.
 2. You've [set up your build environment](newbs_getting_started.md?id=environment-setup).
 
+
 ## Your fork's master: Update Often, Commit Never
 
 It is highly recommended for QMK development, regardless of what is being done or where, to keep your `master` branch updated, but ***never*** commit to it. Instead, do all your changes in a development branch and issue pull requests from your branches when you're developing.
@@ -46,8 +47,7 @@ git push origin master
 
 This switches you to your `master` branch, retrieves the refs from the QMK repo, downloads the current QMK `master` branch to your computer, and then uploads it to your fork.
 
-
-## Making Changes
+### Making Changes
 
 To make changes, create a new branch by entering:
 
@@ -79,6 +79,85 @@ git commit -m "My commit message."
 
 !> If you've changed a lot of files, but all the files are part of the same change, you can use `git add .` to add all the changed files that are in your current directory, rather than having to add each file individually.
 
-## Publishing Your Changes
+### Publishing Your Changes
 
 The last step is to push your changes to your fork. To do this, enter `git push`. Git now publishes the current state of `dev_branch` to your fork.
+
+
+## Resolving Merge Conflicts
+
+Sometimes when your work in a branch takes a long time to complete, changes that have been made by others conflict with changes you have made to your branch when you open a pull request. This is called a *merge conflict*, and is what happens when multiple people edit the same parts of the same files.
+
+### Rebasing Your Changes
+
+A *rebase* is Git's way of taking changes that were applied at one point, reversing them, and then applying the same changes to another point. In the case of a merge conflict, you can rebase your branch to grab the changes that were made between when you created your branch and the present time.
+
+To start, run the following:
+
+```
+git fetch upstream
+git rev-list --left-right --count HEAD...upstream/master
+```
+
+The `git rev-list` command entered here returns the number of commits that differ between the current branch and QMK's master branch. We run `git fetch` first to make sure we have the refs that represent the current state of the upstream repo. The output of the `git rev-list` command entered returns two numbers:
+
+```
+$ git rev-list --left-right --count HEAD...upstream/master
+7       35
+```
+
+The first number represents the number of commits on the current branch since it was created, and the second number is the number of commits made to `upstream/master` since the current branch was created, and thus, the changes that are not recorded in the current branch.
+
+Now that the current states of both the current branch and the upstream repo are known, we can start a rebase operation:
+
+```
+git rebase upstream/master
+```
+
+This tells Git to undo the commits on the current branch, and then reapply them against QMK's master branch.
+
+```
+$ git rebase upstream/master
+First, rewinding head to replay your work on top of it...
+Applying: Commit #1
+Using index info to reconstruct a base tree...
+M       conflicting_file_1.txt
+Falling back to patching base and 3-way merge...
+Auto-merging conflicting_file_1.txt
+CONFLICT (content): Merge conflict in conflicting_file_1.txt
+error: Failed to merge in the changes.
+hint: Use 'git am --show-current-patch' to see the failed patch
+Patch failed at 0001 Commit #1
+
+Resolve all conflicts manually, mark them as resolved with
+"git add/rm <conflicted_files>", then run "git rebase --continue".
+You can instead skip this commit: run "git rebase --skip".
+To abort and get back to the state before "git rebase", run "git rebase --abort".
+```
+
+This tells us that we have a merge conflict, and gives the name of the file with the conflict. Open the conflicting file in your text editor, and somewhere in the file, you'll find something like this:
+
+```
+<<<<<<< HEAD
+<p>For help with any issues, email us at support@webhost.us.</p>
+=======
+<p>Need help? Email support@webhost.us.</p>
+>>>>>>> Commit #1
+```
+
+The line `<<<<<<< HEAD` marks the beginning of a merge conflict, and the `>>>>>>> Commit #1` line marks the end, with the conflicting sections separated by `=======`. The part on the `HEAD` side is from the QMK master version of the file, and the part marked with the commit message is from the current branch and commit.
+
+Because Git tracks *changes to files* rather than the contents of the files directly, if Git can't find the text that was in the file previous to the commit that was made, it won't know how to edit the file. Re-editing the file will solve the conflict. Make your changes, and then save the file.
+
+```
+<p>Need help? Email support@webhost.us.</p>
+```
+
+Now run:
+
+```
+git add conflicting_file_1.txt
+git rebase --continue
+```
+
+Git logs the changes to the conflicting file, and continues applying the commits from our branch until it reaches the end.