Add information for git on how to delete big file history to reduce size of repository

Documents/git/removing-large-files-git-bfg.md

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+# Removing Large Files from Git History with BFG
+
+Source: https://www.phase2technology.com/blog/removing-large-files-git-bfg
+
+On a recent project, our Git repo had ballooned to over **3GB**. The .git directory alone was **2.7GB**. This was slowing down builds and annoying the heck out of developers.
+
+Turns out, a [tool called BFG](https://rtyley.github.io/bfg-repo-cleaner/) makes it dead simple to clean large files out of your Git history. It does this without actually deleting the files themselves from the latest commit. Here's a quick walkthrough on putting your Git repo on a diet using BFG.
+
+
+## Step 1: Install the BFG cli tool
+
+If you're on a Mac, run `brew install bfg`, but note that it'll prompt you to install Java first if you don't have it yet.
+
+You can also [download it directly](https://rtyley.github.io/bfg-repo-cleaner/#download).
+
+
+## Step 2: Clone your repo as a mirror
+
+Run this to clone your repo as a mirror.
+
+`git clone --mirror git://example.com/your-repo.git`
+
+The `--mirror` flag means that it doesn't actually download any of the files from your codebase. It downloads the `.git` directory contents into the top level, so it looks a little funky at first.
+
+
+## Step 3: Back up your repo
+
+Just in case, now is a good idea to back up your repo to a separate location so that you can restore from it if needed.
+
+`cp -r your-repo.git your-repo-backup.git`
+
+
+## Step 4: Run BFG to remove large blobs
+
+In BFG, you have 3 main options for clearing out large files from your Git history.
+
+*Note: "blobs" are the objects that store file contents in Git.*
+
+
+### Option 1: Strip blobs bigger than a specified size
+
+In this case, you're telling BFG to remove any blobs from history that are larger than a specified size. For example, to strip out any blobs bigger than 10MB, you run:
+
+`bfg --strip-blobs-bigger-than 10M your-repo.git`
+
+
+### Option 2: Strip the biggest blobs, limited to a specified number
+
+If you'd rather just strip the biggest blobs regardless of how large they are, BFG makes that easy:
+
+`bfg --strip-biggest-blobs 100 your-repo.git`
+
+This command will strip the 100 largest blobs from your repo history.
+
+
+### Option 3: Strip specific blobs, specified by IDs
+
+If you know of specific files you want to get rid of, you can take this approach. In this case, you'll pass in a text file that contains the list of blob IDs you want to strip.
+
+`bfg --strip-blobs-with-ids blobs.txt your-repo.git`
+
+You can use [a one-liner like this](https://gist.github.com/rtyley/4202730) like this to find the IDs of the largest blobs.
+
+
+## Protecting specific branches
+
+BFG is very good at making sure that it doesn't touch any of the files on your HEAD. It only adjusts your history, not the files in your latest commit.
+
+But if you have other branches you want to make sure you protect, you can do that with the `--protect-blobs-from` flag:
+
+`bfg --protect-blobs-from master,dev,stage --strip-biggest-blobs 100 your-repo.git`
+
+
+## Step 5: Expire and prune your repo
+
+You're removing things with BFG. Now it's time to expire and prune your git history to reflect your changes. Here's how you'd do that:
+
+`cd your-repo.git git reflog expire --expire=now --all && git gc --prune=now --aggressive`
+
+Note that this command can take **a long time** depending on your repo size. So it's best to make sure you're done running BFG first. You only want to have to run this command one time.
+
+
+## Step 6: Check your repo size
+
+Verification time! Did the repo shrink? If not, then you probably missed a step or didn't remove the correct files.
+
+
+## Step 7: Push your changes
+
+Now you're ready to push all your updates so that everyone can enjoy the new, slimmer repo you have fashioned.
+
+`git push`
+
+And that's that! Your repo should be smaller, without any noticeable negative effects. Thanks BFG!