Fix typos and grammatical errors in INSTALL documentation (apache#40417)

Corrected several typographical and grammatical errors in the INSTALL documentation.
These changes improve the clarity and readability of the
instructions. Specific changes include correcting "CPyhon" to "CPython"
and standardizing the capitalization of "Airflow".

Author: myeunee

INSTALL

@@ -3,8 +3,8 @@ INSTALL / BUILD instructions for Apache Airflow
 Basic installation of Airflow from sources and development environment setup
 ============================================================================
 
-This is a generic installation method that requires minimum standard tools to develop airflow and
-test it in a local virtual environment (using standard CPyhon installation and `pip`).
+This is a generic installation method that requires minimum standard tools to develop Airflow and
+test it in a local virtual environment (using standard CPython installation and `pip`).
 
 Depending on your system, you might need different prerequisites, but the following
 systems/prerequisites are known to work:
@@ -61,7 +61,7 @@ Once you have a suitable Python version installed, you can create a virtualenv a
 
 ## Installing Airflow locally
 
-Installing airflow locally can be done using pip - note that this will install "development" version of
+Installing Airflow locally can be done using pip - note that this will install "development" version of
 Airflow, where all providers are installed from local sources (if available), not from `pypi`.
 It will also not include pre-installed providers installed from PyPI. If you install from sources of
 just Airflow, you need to install separately each provider you want to develop. If you install