Introduce total mass macro.

Allows the examintion of the mass of materials and component in the simulation geometries.

macro/geometry/README.md

@@ -203,7 +203,6 @@ Allows to run the `check_radlen` script on sets of geometries present in the sub
   Example for a version: `./macro/geometry/check_radlen_bulk.sh v22a` \
   Special tags which cannot be used in this way: `git`, `all`, `main`
 
-
 ---
 
 ## examine_materials.C
@@ -241,4 +240,17 @@ The lists of expected (known and ignored) overlaps are defined in 4 vectors at t
    ```
    root -l -b -q 'check_overlaps.C("<full filename with path>.geo.root", "<full filename with path for alignment matrices>.root")'
    ```
+=======
+---
+
+## total_mass.C
+
+Measures the total mass of the a geometry and setup, via a random dart method. Basic command may be run by, e.g., 
+
+```
+root -q total_mass.C'
+```
+
+This will output the total mass of each material in the setup.
+