hg: add page (#1728)

pages/common/hg.md

@@ -0,0 +1,19 @@
+# hg
+
+> A command line interface for Mercurial, a distributed source control management system.
+
+- Execute Mercurial command:
+
+`hg {{command}}`
+
+- Call general help:
+
+`hg help`
+
+- Call help on a command:
+
+`hg help {{command}}`
+
+- Check the Mercurial version:
+
+`hg --version`