adding instructions to port instrumentation (#26)

Adding some instructions on how to port from the reference directory. More updates will be needed as tests are added. 

Co-Authored-By: Hector Hernandez <39923391+hectorhdzg@users.noreply.github.com>

Co-authored-by: Mauricio Vásquez <mauricio@kinvolk.io>
Co-authored-by: Hector Hernandez <39923391+hectorhdzg@users.noreply.github.com>

_template/setup.py

@@ -0,0 +1,42 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import os
+
+import setuptools
+
+BASE_DIR = os.path.dirname(__file__)
+VERSION_FILENAME = os.path.join(
+    # REPLACE ME: the path to the version file e.g
+    # BASE_DIR, "src", "opentelemetry", "instrumentation", "sqlalchemy", "version.py"
+    BASE_DIR,
+    "src",
+    "opentelemetry",
+    "instrumentation",
+    "<REPLACE ME>",
+    "version.py",
+)
+PACKAGE_INFO = {}
+with open(VERSION_FILENAME) as f:
+    exec(f.read(), PACKAGE_INFO)
+
+setuptools.setup(
+    version=PACKAGE_INFO["__version__"],
+    entry_points={
+        "opentelemetry_instrumentor": [
+            # REPLACE ME: the entrypoint for the instrumentor e.g
+            # "sqlalchemy = opentelemetry.instrumentation.sqlalchemy:SQLAlchemyInstrumentor"
+            "<REPLACE ME> = opentelemetry.instrumentation.<REPLACE>"
+        ]
+    },
+)