Add Determine The Hash Id For A Blob as a git til.

README.md

@@ -35,6 +35,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Checkout Previous Branch](git/checkout-previous-branch.md)
 - [Clean Out All Local Branches](git/clean-out-all-local-branches.md)
 - [Delete All Untracked Files](git/delete-all-untracked-files.md)
+- [Determine The Hash Id For A Blob](git/determine-the-hash-id-for-a-blob.md)
 - [Dry Runs in Git](git/dry-runs-in-git.md)
 - [Excluding Files Locally](git/excluding-files-locally.md)
 - [Ignore Changes To A Tracked File](git/ignore-changes-to-a-tracked-file.md)

git/determine-the-hash-id-for-a-blob.md

@@ -0,0 +1,16 @@
+# Determine The Hash Id For A Blob
+
+Git's `hash-object` command can be used to determine what hash id will be
+used by git when creating a blob in its internal file system.
+
+```bash
+$ echo 'Hello, world!' > hello-world
+$ git hash-object hola
+af5626b4a114abcb82d63db7c8082c3c4756e51b
+```
+
+When a commit happens, git will generate this digest (hash id) based on the
+contents of the file. The name and location of the file don't matter, just
+the contents. This is the magic of git. Anytime git needs to store a blob,
+it can quickly match against the hash id in order to avoid storing duplicate
+blobs.