Advise on how to get started with a README

Fixes issue #16 

Point readers at how-we-work/explainer and provide some copy-pastable verbiage for linking to HTML via GH pages.

Author: mikesamuel

README.md

@@ -29,9 +29,32 @@ Follow these steps:
       chmod +x .git/hooks/post-rewrite
       ```
 -->
+  1.  ["How to write a good explainer"][explainer] explains how to make a good first impression.
+
+      > Each TC39 proposal should have a `README.md` file which explains the purpose
+      > of the proposal and its shape at a high level.
+      >
+      > ...
+      >
+      > The rest of this page can be used as a template ...
+
+      Your explainer can point readers to the `index.html` generated from `spec.emu`
+      via markdown like
+
+      ```markdown
+      You can browse the [ecmarkup output](https://ACCOUNT.github.io/PROJECT/)
+      or browse the [source](https://github.com/ACCOUNT/PROJECT/blob/master/spec.emu).
+      ```
+
+      where *ACCOUNT* and *PROJECT* are the first two path elements in your project's Github URL.
+      For example, for github.com/**tc39**/**template-for-proposals**, *ACCOUNT* is "tc39"
+      and *PROJECT* is "template-for-proposals".
+
 
 ## Maintain your proposal repo
 
   1. Make your changes to `spec.emu` (ecmarkup uses HTML syntax, but is not HTML, so I strongly suggest not naming it ".html")
   1. Any commit that makes meaningful changes to the spec, should run `npm run build` and commit the resulting output.
   1. Whenever you update `ecmarkup`, run `npm run build` and commit any changes that come from that dependency.
+  
+  [explainer]: https://github.com/tc39/how-we-work/blob/master/explainer.md