rename test step and update readme

Author: Parzival-3141

README.md

@@ -2,7 +2,7 @@
 This is [libgit2](https://libgit2.org/) packaged using Zig's build system.
 Currently only supports Windows and Linux targets.
 
-While libgit2 supports many different options for system dependencies, I've opted to use [MbedTLS](https://www.trustedfirmware.org/projects/mbed-tls/) on Linux for TLS, crypto, and certificate support. SSH support is optional, and is provided by [libssh2](https://libssh2.org/).
+While libgit2 supports many different options for system dependencies, I've opted to use [MbedTLS](https://www.trustedfirmware.org/projects/mbed-tls/) by default on Linux for TLS, crypto, and certificate support. You can replace MbedTLS with OpenSSL if you prefer. SSH support is optional, and is provided by [libssh2](https://libssh2.org/). 
 All other dependencies are bundled in the source tree and compiled statically.
 
 ## Usage
@@ -17,6 +17,7 @@ const libgit2_dep = b.dependency("libgit2", .{
     .target = target,
     .optimize = optimize,
     .@"enable-ssh" = true, // optional ssh support via libssh2
+    .@"enable-openssl" = true, // use openssl instead of mbedtls
 });
 your_compile_step.linkLibrary(libgit_dep.artifact("git2"));
 ```

build.zig

@@ -362,7 +362,7 @@ pub fn build(b: *std.Build) !void {
         examples_step.dependOn(&example_run.step);
     }
 
-    const tests_step = b.step("run-tests", "Tests");
+    const tests_step = b.step("test", "Run unit tests");
     {
         const tests = b.addTest(.{
             .root_source_file = b.path("tests/main.zig"),