Fixed typos for SOURCE.md (geonetwork#7384)

Author: SuperOctocat

software_development/SOURCE.md

@@ -18,7 +18,7 @@ mvn clean install -DskipTests
 Submodules
 ----------
 
-GeoNetwork use submodules, these were initiziled by the ``--recursive`` option when cloning the repository.
+GeoNetwork use submodules, these were initialized by the ``--recursive`` option when cloning the repository.
 
 If you missed using ``--recursive`` run the following:
 
@@ -28,7 +28,7 @@ git submodule init
 git submodule update
 ```
 
-Submodules are used to keep track of externals dependencies. It is necessary to init and update them after a branch change:
+Submodules are used to keep track of external dependencies. It is necessary to init and update them after a branch change:
 
 
 ```