README.md: note current minimum tested Git version

Our README file contains a brief note in its "Example Usage" section
stating that Git LFS requires a Git version higher than 1.8.2 on
Linux and 1.8.5 on macOS.  This statement dates from commit
59a49b0 in PR git-lfs#412 in 2015, and so
is relatively out of date.

In particular, when we added support for the "git lfs migrate" command
in PR git-lfs#2353, the actual minimum supported version of Git was changed
from 1.8.x to 1.9.0 (in commit 1d0e834)
and then to 2.0.0 (in commit 5aea841).

These changes were made to the Travis CI configuration in use at the time,
and later migrated to our current GitHub Actions CI workflow in commit
c32820806229c3f42364d989f7a8597f73cb107ba of PR git-lfs#3808.  This workflow
continues to run our Git LFS test suite using Git 2.0.0.

We therefore now update our README file to remove the outdated note
about Git 1.8.x versions, and add a paragraph to the "Limitations"
section which documents the current minimum supported Git version of
2.0.0 but also strongly advises the use of a more recent Git version.

README.md

@@ -140,8 +140,6 @@ To https://github.com/git-lfs/git-lfs-test
    67fcf6a..47b2002  main -> main
 ```
 
-Note: Git LFS requires at least Git 1.8.2 on Linux or 1.8.5 on macOS.
-
 ### Uninstalling
 
 If you've decided that Git LFS isn't right for you, you can convert your
@@ -163,6 +161,10 @@ know in an issue, and we'll definitely try to help or get it fixed.
 Git LFS maintains a list of currently known limitations, which you can find and
 edit [here](https://github.com/git-lfs/git-lfs/wiki/Limitations).
 
+Current releases of Git LFS will work with Git versions as early as
+Git 2.0.0.  However, for best performance, using a recent version of Git
+is highly recommended.
+
 Git LFS source code utilizes Go modules in its build system, and therefore this
 project contains a `go.mod` file with a defined Go module path.  However, we
 do not maintain a stable Go language API or ABI, as Git LFS is intended to be