[Patch] Readme.md: Update EDK II CI build branch name

["Michael D Kinney" <michael.d.kinney@intel.com>]

    https://bugzilla.tianocore.org/show_bug.cgi?id=2315

Update Readme.md to indicate that that status badges are for
the edk2/master branch.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
---
 Readme.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Readme.md b/Readme.md
index acbcca88d3..594f16b207 100644
--- a/Readme.md
+++ b/Readme.md
@@ -17,7 +17,7 @@ for the UEFI and PI specifications from www.uefi.org.
   <tr>
     <td>Windows</td>
     <td>VS2019</td>
-    <td>edk2-ci</td>
+    <td>master</td>
     <td>
       <a  href="https://dev.azure.com/tianocore/edk2-ci/_build/latest?definitionId=32&branchName=master">
       <img src="https://dev.azure.com/tianocore/edk2-ci/_apis/build/status/Windows%20VS2019%20CI?branchName=master"/></a>
@@ -34,7 +34,7 @@ for the UEFI and PI specifications from www.uefi.org.
   <tr>
     <td>Ubuntu</td>
     <td>GCC</td>
-    <td>edk2-ci</td>
+    <td>master</td>
     <td>
       <a  href="https://dev.azure.com/tianocore/edk2-ci/_build/latest?definitionId=31&branchName=master">
       <img src="https://dev.azure.com/tianocore/edk2-ci/_apis/build/status/Ubuntu%20GCC5%20CI?branchName=master"/></a>
-- 
2.21.0.windows.1