vim:plugs: Add vim-obsession

> obsession.vim: continuously updated session files

.gitmodules

@@ -68,6 +68,9 @@
 [submodule "vim-lastplace"]
 	path = .config/vim/pack/plugins/opt/vim-lastplace
 	url = https://github.com/farmergreg/vim-lastplace
+[submodule "vim-obsession"]
+	path = .config/vim/pack/plugins/opt/vim-obsession
+	url = https://github.com/tpope/vim-obsession
 [submodule "vim-surround"]
 	path = .config/vim/pack/plugins/opt/vim-surround
 	url = https://github.com/tpope/vim-surround