docs: Improve sentence structure and clarity in quickstart guide

Author: tony

docs/quickstart.md

@@ -4,13 +4,13 @@
 
 ## Installation
 
-For latest official version:
+For the latest official version:
 
 ```console
 $ python -m pip install libvcs
 ```
 
-Upgrading:
+Upgrading to the latest version:
 
 ```console
 $ python -m pip install --upgrade libvcs
@@ -20,9 +20,9 @@ $ python -m pip install --upgrade libvcs
 
 ### Developmental releases
 
-New versions of libvcs are published to PyPI as alpha, beta, or release candidates. In their
-versions, you will see notations like `a1`, `b1`, and `rc1`, respectively. For example, `1.10.0b4` would mean
-the 4th beta release of `1.10.0` before general availability.
+New versions of libvcs are published to PyPI as alpha, beta, or release candidates. These versions
+are marked with notations like `a1`, `b1`, and `rc1`, respectively. For example, `1.10.0b4` indicates
+the 4th beta release of version `1.10.0` before its general availability.
 
 Installation options: