Add cheatsheet for hg

Mercurial is extensively used as a version control system, as an option to Git, so I'm adding its cheatsheet.

cheat/cheatsheets/hg

@@ -0,0 +1,20 @@
+# Clone a directory
+hg clone
+
+# Add files to hg tracker
+hg add filename
+
+# Add all files in a folder to hg tracker
+hg add folder/
+
+# Create a commit with all tracked changes and a message
+hg commit -m "message"
+
+# Push commits to source repository
+hg push
+
+# Pull changes from source repository
+hg pull
+
+# Rebase local commits to disambiguate with remote repository
+hg pull --rebase