Add git blame ignore file (#177)

.git-blame-ignore-revs

@@ -0,0 +1,2 @@
+8a88efcccd35474d8affaef53cf16d799f9ef65b
+c3a5d683f90e92a8b37acac640bddbc5e3a54b8c

CONTRIBUTING.md

@@ -307,3 +307,27 @@ the following steps:
 
 The `stable/*` branches should only receive changes in the form of bug
 fixes.
+
+## Dealing with the git blame ignore list
+
+In the qiskit-nature repository we maintain a list of commits for git blame
+to ignore. This is mostly commits that are code style changes that don't
+change the functionality but just change the code formatting (for example,
+when we migrated to use black for code formatting). This file,
+`.git-blame-ignore-revs` just contains a list of commit SHA1s you can tell git
+to ignore when using the `git blame` command. This can be done one time
+with something like
+
+```
+git blame --ignore-revs-file .git-blame-ignore-revs qiskit_nature/version.py
+```
+
+from the root of the repository. If you'd like to enable this by default you
+can update your local repository's configuration with:
+
+```
+git config blame.ignoreRevsFile .git-blame-ignore-revs
+```
+
+which will update your local repositories configuration to use the ignore list
+by default.