README: Document workflow (#21)

README.md

@@ -10,13 +10,16 @@ Example `.pkg` file:
       commit=3eca62d66c7c9a2ca97dc8381299d911978b9fb2
 
 ## Useful commands
-After invoking `CMake`, the `pkg` binary executable can be found in `build/dl/`.
+
+When using [pkg.cmake](https://github.com/motis-project/motis/blob/master/cmake/pkg.cmake), the `pkg` binary executable
+will be downloaded after invoking `cmake` if pkg is not already installed on the system. It can then be found in `build/dl/`.
 
 ### Displaying the dependency tree
 
     pkg -s
 
 ### Syncing deps/
+
 After updating a commit ID in the `.pkg` file,
 you can `pkg -l` to establish the dependency tree state described in the `.pkg` file.
 Effectively, `git` repositories will be updated in `deps/`.
@@ -25,3 +28,15 @@ You can use `-f` to force checkout the commits.
 
 > [!WARNING]
 > This will override the changes you made, so be careful.
+
+### Workflow
+
+You can work on dependencies directly in the `deps` directory.
+`pkg` will try to not get in your way while you are working on a dependency
+by not changing the state of the dependency's checkout when
+
+ * There are uncommitted changes on top of the commit specified in `.pkg`
+ * There are unpushed commits on the currently checked out branch
+
+Don't forget to update the dependency commit hash in `.pkg` to your new commit after you are done!
+Otherwise `pkg` will try to check out the pinned commit.