implement a build script

Signed-off-by: RJ Catalano <rj@monax.io>

docs/installing-solidity.rst

@@ -198,7 +198,13 @@ Building Solidity is quite similar on Linux, macOS and other Unices:
     cd build
     cmake .. && make
 
-And even on Windows:
+or even easier:
+
+.. code:: bash
+
+    ./scripts/build.sh
+
+And even for Windows:
 
 .. code:: bash
 
@@ -251,4 +257,4 @@ Example:
 3. a breaking change is introduced - version is bumped to 0.5.0
 4. the 0.5.0 release is made
 
-This behaviour works well with the version pragma.
+This behaviour works well with the version pragma.