Document option "core.sha1Implementation" introduced in 59029aec

Bug: 580310
Change-Id: I10f3d6f6b5af7ab96683994c9cbd85e6c18a5084

Documentation/config-options.md

@@ -42,6 +42,7 @@ For details on native git options see also the official [git config documentatio
 | `core.precomposeUnicode` | `true` on Mac OS | ✅ | MacOS only. When `true`, JGit reverts the unicode decomposition of filenames done by Mac OS. |
 | `core.quotePath` | `true` | ✅ | Commands that output paths (e.g. ls-files, diff), will quote "unusual" characters in the pathname by enclosing the pathname in double-quotes and escaping those characters with backslashes in the same way C escapes control characters (e.g. `\t` for TAB, `\n` for LF, `\\` for backslash) or bytes with values larger than `0x80` (e.g. octal `\302\265` for "micro" in UTF-8). |
 | `core.repositoryFormatVersion` | `1` | ⃞ | Internal version identifying the repository format and layout version. Don't set manually. |
+| `core.sha1Implementation` | `java` | ⃞ | Choose the SHA1 implementation used by JGit. Set it to `java` to use JGit's Java implementation which detects SHA1 collisions if system property `org.eclipse.jgit.util.sha1.detectCollision` is unset or `true`. Set it to `jdkNative` to use the native implementation available in the JDK, can also be set using system property `org.eclipse.jgit.util.sha1.implementation`. If both are set the system property takes precedence. Performance of `jdkNative` is around 10% higher than `java` when `detectCollision=false` and 30% higher when `detectCollision=true`.|
 | `core.streamFileThreshold` | `50 MiB` | ⃞ | The size threshold beyond which objects must be streamed. |
 | `core.supportsAtomicFileCreation` | `true` | ⃞ | Whether the filesystem supports atomic file creation. |
 | `core.symlinks` | Auto detect if filesystem supports symlinks| ✅ | If false, symbolic links are checked out as small plain files that contain the link text. |