fixed broken link in readme

[changfubai]

What is the purpose of the change

to fix broken link in readme

Brief changelog

2 sample urls and 3 guide link

[codecov-io]

Codecov Report

Merging #7037 (fde73cc) into master (e84cdc2) will increase coverage by 0.08%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #7037      +/-   ##
============================================
+ Coverage     59.41%   59.49%   +0.08%     
  Complexity      508      508              
============================================
  Files          1028     1028              
  Lines         41519    41641     +122     
  Branches       6037     6080      +43     
============================================
+ Hits          24668    24775     +107     
- Misses        14107    14117      +10     
- Partials       2744     2749       +5     

Impacted Files	Coverage Δ	Complexity Δ
.../remoting/transport/netty4/NettyServerHandler.java	61.36% <0.00%> (-9.10%)	0.00% <0.00%> (ø%)
...e/dubbo/remoting/transport/netty/NettyChannel.java	55.68% <0.00%> (-4.55%)	20.00% <0.00%> (-1.00%)
...dubbo/remoting/exchange/support/DefaultFuture.java	88.03% <0.00%> (-4.28%)	0.00% <0.00%> (ø%)
...pache/dubbo/registry/support/AbstractRegistry.java	79.62% <0.00%> (-1.49%)	0.00% <0.00%> (ø%)
...he/dubbo/registry/multicast/MulticastRegistry.java	67.12% <0.00%> (-0.93%)	0.00% <0.00%> (ø%)
...g/apache/dubbo/registry/consul/ConsulRegistry.java	60.00% <0.00%> (-0.59%)	31.00% <0.00%> (ø%)
...rg/apache/dubbo/common/timer/HashedWheelTimer.java	63.57% <0.00%> (-0.35%)	0.00% <0.00%> (ø%)
...ava/org/apache/dubbo/config/ServiceConfigBase.java	59.53% <0.00%> (+0.57%)	0.00% <0.00%> (ø%)
...he/dubbo/rpc/protocol/hessian/HessianProtocol.java	69.87% <0.00%> (+2.40%)	9.00% <0.00%> (ø%)
...he/dubbo/remoting/transport/netty/NettyServer.java	73.68% <0.00%> (+3.50%)	9.00% <0.00%> (+1.00%)
... and 2 more

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