Add install instructions.

docs/source/install.rst

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+Installation
+============
+
+Petrelic offers some Python binding for Relic. This library needs to be build
+with some precise compilation flags. To use it with petrelic, a script to set
+the correct compilation option is provided in `wheel/00custom.sh`, and is to be
+run as the others presets for Relic. Also, the CMakeLists.txt of Relic needs to
+be patched to take a compilation flag in consideration. The patch is provided
+in: `wheel/CMakeLists.patch` and can be applied as any other patch::
+    cd ${PATH_TO_RELIC}
+    patch CMakeLists.txt "${PATH_TO_PETRELIC}/wheel/CMakeLists.patch"
+
+Relic depends among other on GMP, which need to be installed either from
+sources or from your distribution.
+
+Some script to build Wheel packages are provided. They rely on manylinux2010
+and Docker to run properly. Depending on your machine, building this wheel
+takes about 10 minutes. To build this local wheel, run::
+    cd ${PATH_TO_PETRELIC}
+    sh build.sh
+
+The resulting wheels contains Relic and GMP, and can be installed with pip as
+normal::
+    pip install petrelic-0.0.0-cp36-cp36m-manylinux2010_x86_64.whl
+
+
+In the future, to simplify this installation, some Wheel packages are going to
+provided for Linux and Mac OS X systems containing the embedded libraries Relic
+and GMP, which will be able to be downloaded and installed with pip::
+    pip install petrelic