doc: make the commands in README.md properly aligned

The commands in README.md are aligned using one tab or eight spaces,
the github markdown engine not handle this properly, so using one tab
universely.

Signed-off-by: Yao Zongyou <[email protected]>

README.md

@@ -65,40 +65,40 @@ correct path to the checkout.
 
 To build only certain targets use:
 
-        make [target name]
+	make [target name]
 
 To install:
 
-        make install
+	make install
 
 ### CMake Options
 
 If you run the `cmake` command by hand, there are many options you can
 set with "-D". For example the option to build the RADOS Gateway is
 defaulted to ON. To build without the RADOS Gateway:
 
-        cmake -DWITH_RADOSGW=OFF [path to top level ceph directory]
+	cmake -DWITH_RADOSGW=OFF [path to top level ceph directory]
 
 Another example below is building with debugging and alternate locations 
 for a couple of external dependencies:
 
-        cmake -DLEVELDB_PREFIX="/opt/hyperleveldb" -DOFED_PREFIX="/opt/ofed" \
-        -DCMAKE_INSTALL_PREFIX=/opt/accelio -DCMAKE_C_FLAGS="-O0 -g3 -gdwarf-4" \
-        ..
+	cmake -DLEVELDB_PREFIX="/opt/hyperleveldb" -DOFED_PREFIX="/opt/ofed" \
+	-DCMAKE_INSTALL_PREFIX=/opt/accelio -DCMAKE_C_FLAGS="-O0 -g3 -gdwarf-4" \
+	..
 
 To view an exhaustive list of -D options, you can invoke `cmake` with:
 
-        cmake -LH
+	cmake -LH
 
 If you often pipe `make` to `less` and would like to maintain the
 diagnostic colors for errors and warnings (and if your compiler
 supports it), you can invoke `cmake` with:
 
-        cmake -DDIAGNOSTICS_COLOR=always ..
+	cmake -DDIAGNOSTICS_COLOR=always ..
 
 Then you'll get the diagnostic colors when you execute:
 
-        make | less -R
+	make | less -R
 
 Other available values for 'DIAGNOSTICS_COLOR' are 'auto' (default) and
 'never'.
@@ -159,8 +159,8 @@ When failures occur, look in build/Testing/Temporary for logs.
 To build and run all tests and their dependencies without other
 unnecessary targets in Ceph:
 
-        cd build
-        make check -j$(nproc)
+	cd build
+	make check -j$(nproc)
 
 To run an individual test manually, run `ctest` with -R (regex matching):