Merge pull request #141 from goyalankit/master

adding gem command

common/gem.md

@@ -0,0 +1,23 @@
+#gem
+
+> Interact with the package manager for the Ruby programming language.
+
+- Install latest version of a gem
+
+`gem install {{gemname}}`
+
+- Install specific version of a gem
+
+`gem install -v=0.0.15`
+
+- Update a gem
+
+`gem update {{gemname}}`
+
+- List all gems
+
+`gem list`
+
+- Uninstall a gem
+
+`gem uninstall {{gemname}}`