Add automatic merging guidelines to the README. (#106)

Copied from JuliaRegistries/General#3673
with minor formatting changes (a bit more compact), added
clarifications for all questions which came up in the related
discussion
https://discourse.julialang.org/t/announcement-automatic-merging-for-the-general-registry/29961

README.md

@@ -9,6 +9,47 @@ The [General](https://github.com/JuliaRegistries/General) registry uses Registry
 
 You can also use RegistryCI for your own Julia package registry.
 
+## Automatic merging guidelines
+
+These guidelines are intended not as requirements for packages but as very conservative guidelines, which, if your new package or new version of a package meets them, it may be automatically merged.
+
+Note that commenting on a pull request will automatically disable automerging on that pull request. Therefore, if you want to leave a comment on a pull request but you still want that pull request to be automerged, please include the text `[noblock]` in your comment.
+
+### New package
+
+1. Normal capitalization
+
+    The package name should match `r"^[A-Z]\w*[a-z][0-9]?$"`, i.e. start with a capital letter, contain ASCII alphanumerics only, end in lowercase.
+
+2. Not too short
+
+    At least five letters. *You can register names shorter than this, but doing so requires someone to approve.*
+
+3. Standard initial version number: one of `0.0.1`, `0.1.0`, `1.0.0`.
+
+4. Repo URL ends with `/$name.jl.git` where `name` is the package name.
+
+### New version of an existing package
+
+1. Sequential version number
+
+    If the last version was `1.2.3` then the next can be `1.2.4`, `1.3.0` or `2.0.0`.
+
+2. [Compat entries](https://julialang.github.io/Pkg.jl/v1/compatibility/) for all dependencies.
+
+    - all `[deps]` should also have `[compat]` entries (and Julia itself)
+    - `[compat]` entries should have upper bounds
+
+    Compat entries are not required for standard libraries.
+
+3. Version can be installed
+
+    Given the proposed changes to the registry, can we resolve and install the new version of the package?
+
+4. Version can be loaded
+
+    Once it's been installed (and built?), can we load the code?
+
 ## Acknowledgements
 
 Dilum Aluthge would like to acknowledge the following: