Very slightly improve readme presentation

- Add a missing period.

- Indicate sh rather than bash as as the language for syntax
  highlighting of shell commands that don't need bash.

I had held off on making that second change in previous revisions
because it would have involved either introducing an inconsistency
or editing the section giving the deprecated signature-checking
instructions. That section was removed in 2671167 (gitpython-developers#1823).

(This also wraps a paragraph where the immediately surrounding text
was wrapped, but that should not affect rendered text, and broader
consistency improvements to Markdown wrapping style are not done.)

Author: EliahKagan

Diff for: README.md

@@ -17,7 +17,7 @@ probably the skills to scratch that itch of mine: implement `git` in a way that
 If you like the idea and want to learn more, please head over to [gitoxide](https://github.com/Byron/gitoxide), an
 implementation of 'git' in [Rust](https://www.rust-lang.org).
 
-*(Please note that `gitoxide` is not currently available for use in Python, and that Rust is required)*
+*(Please note that `gitoxide` is not currently available for use in Python, and that Rust is required.)*
 
 ## GitPython
 
@@ -39,9 +39,9 @@ The project is open to contributions of all kinds, as well as new maintainers.
 
 ### REQUIREMENTS
 
-GitPython needs the `git` executable to be installed on the system and available in your `PATH` for most operations.
-If it is not in your `PATH`, you can help GitPython find it by setting
-the `GIT_PYTHON_GIT_EXECUTABLE=<path/to/git>` environment variable.
+GitPython needs the `git` executable to be installed on the system and available in your
+`PATH` for most operations. If it is not in your `PATH`, you can help GitPython find it
+by setting the `GIT_PYTHON_GIT_EXECUTABLE=<path/to/git>` environment variable.
 
 - Git (1.7.x or newer)
 - Python >= 3.7
@@ -57,7 +57,7 @@ GitPython and its required package dependencies can be installed in any of the f
 
 To obtain and install a copy [from PyPI](https://pypi.org/project/GitPython/), run:
 
-```bash
+```sh
 pip install GitPython
 ```
 
@@ -67,15 +67,15 @@ pip install GitPython
 
 If you have downloaded the source code, run this from inside the unpacked `GitPython` directory:
 
-```bash
+```sh
 pip install .
 ```
 
 #### By cloning the source code repository
 
 To clone the [the GitHub repository](https://github.com/gitpython-developers/GitPython) from source to work on the code, you can do it like so:
 
-```bash
+```sh
 git clone https://github.com/gitpython-developers/GitPython
 cd GitPython
 ./init-tests-after-clone.sh
@@ -85,15 +85,15 @@ On Windows, `./init-tests-after-clone.sh` can be run in a Git Bash shell.
 
 If you are cloning [your own fork](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/about-forks), then replace the above `git clone` command with one that gives the URL of your fork. Or use this [`gh`](https://cli.github.com/) command (assuming you have `gh` and your fork is called `GitPython`):
 
-```bash
+```sh
 gh repo clone GitPython
 ```
 
 Having cloned the repo, create and activate your [virtual environment](https://docs.python.org/3/tutorial/venv.html).
 
 Then make an [editable install](https://pip.pypa.io/en/stable/topics/local-project-installs/#editable-installs):
 
-```bash
+```sh
 pip install -e ".[test]"
 ```
 
@@ -105,7 +105,7 @@ In rare cases, you may want to work on GitPython and one or both of its [gitdb](
 
 If you want to do that *and* you want the versions in GitPython's git submodules to be used, then pass `-e git/ext/gitdb` and/or `-e git/ext/gitdb/gitdb/ext/smmap` to `pip install`. This can be done in any order, and in separate `pip install` commands or the same one, so long as `-e` appears before *each* path. For example, you can install GitPython, gitdb, and smmap editably in the currently active virtual environment this way:
 
-```bash
+```sh
 pip install -e ".[test]" -e git/ext/gitdb -e git/ext/gitdb/gitdb/ext/smmap
 ```
 
@@ -141,33 +141,33 @@ you will encounter test failures.
 
 Ensure testing libraries are installed. This is taken care of already if you installed with:
 
-```bash
+```sh
 pip install -e ".[test]"
 ```
 
 Otherwise, you can run:
 
-```bash
+```sh
 pip install -r test-requirements.txt
 ```
 
 #### Test commands
 
 To test, run:
 
-```bash
+```sh
 pytest
 ```
 
 To lint, and apply automatic code formatting, run:
 
-```bash
+```sh
 pre-commit run --all-files
 ```
 
 To typecheck, run:
 
-```bash
+```sh
 mypy -p git
 ```