Update installation.md

just changed the spelling error in point 3 from "exisint" to "existing", but I suppose "existent" could work as well

docs/website/docs/reference/installation.md

@@ -109,7 +109,7 @@ C:\> .\env\Scripts\activate
 You can now install `dlt` in your virtual environment by running:
 
 ```sh
-# install the newest dlt version or upgrade the exisint version to the newest one
+# install the newest dlt version or upgrade the existing version to the newest one
 pip install -U dlt
 ```
 
@@ -143,4 +143,4 @@ You are now ready to build your first pipeline with `dlt`. Check out these tutor
 - [Load data from a SQL database](../tutorial/sql-database)
 - [Load data from a cloud storage or a file system](../tutorial/filesystem)
 
-Or read a more detailed tutorial on how to build a [custom data pipeline with dlt](../tutorial/load-data-from-an-api.md).
+Or read a more detailed tutorial on how to build a [custom data pipeline with dlt](../tutorial/load-data-from-an-api.md).