Bug 1643098 - Ignore Emacs project sentinel .projectile files. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D78123

.gitignore

@@ -23,6 +23,8 @@ ID
 
 # Emacs directory variable files.
 **/.dir-locals.el
+# Emacs project sentinel files.
+**/.projectile
 
 # User files that may appear at the root
 /.mozconfig*

.hgignore

@@ -20,6 +20,8 @@ compile_commands\.json
 
 # Emacs directory variable files.
 \.dir-locals\.el
+# Emacs project sentinel files.
+\.projectile
 
 # User files that may appear at the root
 ^\.mozconfig