Add .git-blame-ignore-revs

See https://gist.github.com/kateinoigakukun/b0bc920e587851bfffa98b9e279175f2

This is an experiment to see how well it works with various tooling.
I just picked two code style change commits at random:
0077c5da15
110a5877e9

A test case:
- run `git config blame.ignoreRevsFile .git-blame-ignore-revs`
- run `git blame includes/changetags/ChangeTags.php`
- search for 'pass [] or null'
You should see it blamed to a commit that actually has 'array() or null'.

Change-Id: I38725da46642e630564768cce585a4cca1115e50

.git-blame-ignore-revs

@@ -0,0 +1,3 @@
+# mass code style changes - array syntax
+0077c5da15aab081125ee1c72cc4d95225e4ff5f
+110a5877e9e6ebe7a6ecd758f5812f32fc4ef57e