Update README.md

Differential Revision: https://phabricator.twitter.biz/D80441

Author: Adam Cummings

README.md

@@ -5,7 +5,7 @@ Twitter Kit for Unity provides cross-platform support (iOS & Android) for author
 ## Building
 1. Download Twitter Kit frameworks.
 ```
-./scripts/download_ios_frameworks.sh
+./scripts/download_ios_frameworks.sh [version #] (e.g.: ./scripts/download_ios_frameworks.sh 3.1.0)
 ```
 2. Build the Android wrapper.
 ```

scripts/download_ios_frameworks.sh

@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 if [ "$#" -ne 1 ]; then
-  echo "Usage: ./scripts/download_ios_frameworks.sh [version #] (e.g., ./scripts/download_ios_frameworks.sh 3.1.0)" >&2
+  echo "Usage: ./scripts/download_ios_frameworks.sh [version #] (e.g.: ./scripts/download_ios_frameworks.sh 3.1.0)" >&2
   exit 1
 fi