Finish writing the installation instructions.

Add the details about how to resolve the error when the module is not found.

Author: technic960183

docs/source/install.rst

@@ -1,10 +1,35 @@
 Installation
 ============
 
-You can install pycorrelator by cloning the codes:
+You can install **pycorrelator** by cloning the `repository <https://github.com/technic960183/pycorrelator>`_.
 
 .. code-block:: console
 
    $ git clone https://github.com/technic960183/pycorrelator.git
 
-pip install will be supported in the future.
+.. note::
+   ``pip install`` will be supported in the future after we collect enough feedback from the users.
+   Please feel free to try this package and give us feedback. Your feedback is valuable to us.
+
+If you encounter the error:
+
+.. code-block:: console
+
+   ModuleNotFoundError: No module named 'pycorrelator'
+
+Please add the path of the cloned directory to ``sys.path`` by running the following code before importing the module:
+
+.. code-block:: python
+
+   import sys
+   path_to_pycorrelator = '/your_path_to/pycorrelator'
+   sys.path.append(path_to_pycorrelator)
+
+Check if the installation is successful by importing the module:
+
+.. code-block:: python
+
+   from pycorrelator import xmatch
+   print(xmatch.__module__)
+
+If the output is ``pycorrelator.xmatch``, congratulations! You have successfully installed **pycorrelator**.

docs/source/tutorial/duplicates_removal.rst

@@ -50,7 +50,7 @@ Expected output::
           5        10.690 -41.269      2400        5     3
           7        10.689 -41.269      2700        5     2
 
-Here I set the tolerance to 0.01, which means that objects with a separation less than 0.01 degrees to any other
+Here we set the tolerance to 0.01, which means that objects with a separation less than 0.01 degrees to any other
 object in the same 'cluster' will be considered as duplicates. You need to adjust this value according to the
 properties of your catalog. The ``'dup_num'`` column shows the number of duplicates in each group, and the
 ``'rank'`` column shows the order of the object in the group sorted by the ranking column.