当git clone之后，直接git pull它会自动匹配一个正确的remote url
是因为在config文件中配置了以下内容：
1 [branch "master"]
2 remote = origin
3 merge = refs/heads/master
表明：
1.git 处于master这个branch下时，默认的remote就是origin；
2.当在master这个brach下使用指定remote和merge的git pull时，使用默认的remote和merge。
但是对于自己建的项目，并用push到远程服务器上，并没有这块内容，需要自己配置。
如果直接运行git pull，会得到如此结果：
1 $ git pull
2 Password:
3 You asked me to pull without telling me which branch you
4 want to merge with, and 'branch.master.merge' in
5 your configuration file does not tell me, either. Please
6 specify which branch you want to use on the command line and
7 try again (e.g. 'git pull <repository> <refspec>').
8 See git-pull(1) for details.
9
10 If you often merge with the same branch, you may want to
11 use something like the following in your configuration file:
12
13 [branch "master"]
14 remote = <nickname>
15 merge = <remote-ref>
16
17 [remote "<nickname>"]
18 url = <url>
19 fetch = <refspec>
20
21 See git-config(1) for details.
在参考[2]中，有这样一段：
Note: at this point your repository is not setup to merge _from_ the remote branch when you type 'git pull'. You can either freshly 'clone' the repository (see "Developer checkout" below), or configure your current repository this way:
1 git remote add -f origin login@git.sv.gnu.org:/srv/git/project.git
2 git config branch.master.remote origin
3 git config branch.master.merge refs/heads/master
因此通过git config进行如下配置：
1 $ git config branch.master.remote origin
2 $ git config branch.master.merge refs/heads/master
或者加上--global选项，对于全部项目都使用该配置。
执行完以上 命令，在config文件中配置了以下内容：
1 [branch "master"]
2 remote = origin
3 merge = refs/heads/master
============================
假如 当前 仓库有 两个 分支，master 和 test1，当我们 执行了 以下 两条命令之后：
git config branch.test1.remote origin
git config branch.test1.merge refs/heads/test1
将在 在config文件中配置了以下内容：
1 [branch "test1"]
2 remote = origin
3 merge = refs/heads/test1