Warn against absolute paths in Documentation/Usage.md (#7059)

Resolves rdar://115726598.

Author: MaxDesiatov

Documentation/Usage.md

@@ -226,9 +226,10 @@ The header file should look like this:
 #include <git2.h>
 ```
 
-**Note:** Alternatively, you can provide an absolute path to `git2.h` provided
-by the library in the `modile.modulemap`. However, doing so might break
-cross-platform compatibility of your project.
+**Note:** Avoiding specifying an absolute path to `git2.h` provided
+by the library in the `module.modulemap`. Doing so will break compatibility of 
+your project between machines that may use a different file system layout or
+install libraries to different paths.
 
 > The convention we hope the community will adopt is to prefix such modules
 > with `C` and to camelcase the modules as per Swift module name conventions.