fix: add snapcraft to README [skip ci]

drew created 

also, rename the extension of the snapcraft config from yml to yaml

Change summary

README.md      | 6 ++++++
snapcraft.yaml | 0 
2 files changed, 6 insertions(+)

Detailed changes

README.md 🔗 

@@ -34,6 +34,12 @@ email-cli
 
 to get started.
 
+### Install using Snap
+
+```bash
+snap install andrinoff.email-cli
+```
+
 ### Build from Source 🔨
 
 Email CLI is written in **Go**. To build it manually: