feat(tools): add one-line Linux installer (curl|bash) with ICU symlink shim + docs

[JaredTweed]

This PR adds tools/install.sh and a small README section to provide a single-line Linux install (curl | bash) that builds Edit from source across popular distros. It does not modify Edit’s code. Instead, it prepares the system so Edit’s existing ICU-based search works reliably by ensuring unversioned ICU SONAMEs are discoverable at runtime. This resolves issue #616.

[JaredTweed]

@microsoft-github-policy-service agree

[lhecker]

I wonder if we should move part of this into the build.rs script.

[JaredTweed]

@lhecker Good idea, i made the corresponding changes