PSA: Link to files at fixed version

[Nicholas Chammas <ni...@gmail.com>]

*TL;DR*: Hit y on any file page on GitHub to update the URL to a permanent
link.

Many of you probably already know this. Here’s a handy tip for the rest.

So you’re on Github and you want to link to a file in an email, PR, or JIRA
report. Or better yet, you want to link to some specific lines in a file.

So you do this:

https://github.com/apache/spark/blob/master/ec2/spark_ec2.py#L805-L841

This is fine until someone changes the file. Now the link doesn’t make
sense because the line numbers are all different.

Instead, you want to do this:

https://github.com/apache/spark/blob/582e5a24c55e8c876733537c9910001affc8b29b/ec2/spark_ec2.py#L805-L841

This link will always make sense.

To get a link like this, you can just press y while you have the file open
on github.com, and GitHub will update the address in your browser bar to a
perma-link (i.e. from the former link to the latter).

Nick
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